The Houses of Parliament, Tower Bridge, Cardiff Castle and other British landmarks will go dark tonight to commemorate the moment the UK entered the First World War.

Everyone in the country is being invited to take part in the Lights Out project by leaving just a single light on or candle burning for an hour from 10pm tonight.

It is inspired by the quote by the then Foreign Secretary, Sir Edward Grey, on the eve of Britain’s entry into the first ever global conflict: “The lamps are going out all over Europe, we shall not see them lit again in our lifetime.”

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In his memoirs, he recalled making the remark while standing at the window of his office in the Foreign Office on 3 August watching the lights being lit along the Mall as dusk fell.

More than 650 events are happening across the UK, including vigils and walks, for the initiative organised by the Government-sponsored 14-18 NOW programme.

The Royal Shakespeare Company, BBC and even GCHQ (in one section) are among those taking part in Lights Out.

A candlelit vigil of prayer, readings and music is being held in Westminster Abbey and separate events are scheduled in Canterbury and other cathedrals and churches.

Shape Created with Sketch. In pictures: A history of the First World War in 100 moments Show all 149 left Created with Sketch. right Created with Sketch. Shape Created with Sketch. In pictures: A history of the First World War in 100 moments 1/149 First World War Supporting troops of the 1st Australian Division walking on a duckboard track near Hooge, in the Ypres Sector Getty Images 2/149 First World War Final moments: The Archduke of Austria Franz Ferdinand with his wife Sophie in Sarajevo minutes before his shooting AP 3/149 First World War Arresting Princip’s fellow conspirator Nedeljko Cabrinovic after a failed attempt to kill the Archduke on the same day Getty Images 4/149 First World War Crowds in central London cheer Britain’s declaration of war on Germany Getty Images 5/149 First World War The innocents: New recruits, with bicycles, training with the British Army in 1914 Getty 6/149 First World War 1914: A lone soldier with a bicycle stands amid the remains of a German motor convoy which lines a country lane after an attack by French field guns in the battle of the Aisne in France Topical Press Agency/Getty Images 7/149 First World War Troubled waters: The Cambridge eight included John Andrew Ritson (fourth from cox) Museum of London, Christina Broom 8/149 First World War John Andrew Ritson (left) Museum of London, Christina Broom 9/149 First World War Dennis Ivor Day Musuem of London; Christina Broom 10/149 First World War German infantry advance through Belgium in August 1914 Getty Images 11/149 First World War Civilians near the Austrian lines in Serbia are strung up – probably as a reprisal for guerrilla resistance to the invaders Miroslav Honzík/Hana Honzíková 12/149 First World War Captured soldiers of the Russian 2nd Army after their defeat at the Battle of Tannenberg Getty Images 13/149 First World War Wounded and exhausted British and Belgian soldiers retreating after the Battle of Mons Getty Images 14/149 First World War Crowds gather outside a recruitment office Getty Images 15/149 First World War French General Joseph Joffre (second right), Commander- in-Chief of the French Armies, and General Michel Joseph Maunoury (right) on the front during the First Battle of the Marne. Six hundred scarlet taxis were requisitioned, at a cost of Fr70,102, to ferry reservist troops to the Battle of the Marne in 1914 Getty Images 16/149 First World War A French firing squad escorts a deserter to his execution in November 1914 Getty 17/149 First World War One of the trenches from which deserters tried to escape Getty 18/149 First World War German soldiers in Wirballen, a border town between the German Reich and Russia Mary Evans Picture Library 19/149 First World War Carl Hans Lody, who spied in Britain Popperfoto/Getty 20/149 First World War Up to 12 million letters a week were sent to the front line via the wooden sorting office hastily set up in Regent’s Park in 1914 Royal Mail 21/149 First World War Survivors from SMS ‘Gneisenau’ in the sea off the Falkland Islands, with HMS ‘Inflexible’ in the background, 8 December 1914 Getty Images 22/149 First World War The ruins of the cloth hall and cathedral in Ypres during WWI Getty Images 23/149 First World War Margot Asquith, the Countess of Oxford and Asquith and the wife of Britain’s wartime leader Getty Images 24/149 First World War A wounded American in a London hospital reads a magazine with a red cross nurse by his bedside. A. R. Coster/Topical Press Agency/Getty Images 25/149 First World War A mass execution by firing squad following the unsuccessful Singapore mutiny of 1915 rebelsindia.com 26/149 First World War Indian soldiers serving in France were known for their fighting spirit Underwood Archives/Getty 27/149 First World War Russian artillery positions outside Przemysl, during the six-month siege of the heavily fortified Austro-Hungarian city, part of present-day Poland Hulton Archive/Getty Images 28/149 First World War Residents assess the damage after Suffolk was rocked by bomb attacks mounted by German Zeppelin Getty 29/149 First World War German infantrymen attack through a cloud of poison gas. By the end of the war, both sides had employed various kinds of gas Getty 30/149 First World War Children of Armenian refugees in a camp Getty 31/149 First World War Armenian civilians being led away by Ottoman soldiers 32/149 First World War A public hanging in Istanbul 33/149 First World War A pile of skulls from the Armenian village of Sheyxalan AFP/Getty 34/149 First World War Allied troops at Anzac Cove (Gaba Tepe) during the Gallipoli campaign Hulton Archive/Getty Images 35/149 First World War Allied troops unloading heavy guns in the Dardanelles Hulton Archive/Getty Images 36/149 First World War Volunteer nurse Florence Farmborough was part of the Russian retreat from Gorlice 37/149 First World War Cunard liner RMS Lusitania, after secret Whitehall misgivings about the official account of one of the most controversial and tragic episodes of the First World War were revealed in newly-released government documents. Almost 70 years after the Cunard liner RMS Lusitania was sunk by a German U-boat off the coast of Ireland, some officials expressed concern that the truth was still being covered up PA Wire 38/149 First World War The RMS Lusitania sailed from New York on 1 May 1915 on her last voyage; the liner was sunk off southern Ireland on 7 May Getty Images 39/149 First World War Welsh Liberal politician and future Prime Minister David Lloyd George (1863 - 1945) enjoys a quiet read of a newspaper in his garden with his faithful dog for company Getty 40/149 First World War French troops line up for inspection on a trench on the Western Front Getty Images 41/149 First World War German military prisoners, at Southend-on-Sea, on their way to Knockaloe Print Collector/Hulton Archive/Getty Images 42/149 First World War The railway line running the length of the access road into Knockaloe, the biggest camp in the British Isles 43/149 First World War Survivors of the sinking in Cobh, Co Cork Getty Images 44/149 First World War Robert Graves (1895-1985), who served on the Western Front from 1915 to 1917 45/149 First World War 2nd Lieutenant John Kipling is thought to have been killed in The Chalk Pit, in Loos, France, on 27 September 1915 Wikimedia Creative Commons 46/149 First World War Laid to rest: Edith Cavell circa 1905 Getty 47/149 First World War Her funeral cortege in London in May 1919 Getty 48/149 First World War George Samson is celebrated on a cigarette card of the time 49/149 First World War Flora Sandes, who rose from private to sergeant-major in the Serbian army, playing chess with her Serbian comrades. After the war ended, she was promoted to lieutenant 50/149 First World War Italian light infantry of the 1st Alpini Regiment on Monte Nero, during the Isonzo campaigns Universal History Archive/UIG/Getty Images 51/149 First World War As Italian as mozzarella cheese: Giuseppe Ungaretti 52/149 First World War French troops under shellfire during the Battle of Verdun Getty Images 53/149 First World War A French soldier is shot during a counter attack Alamy 54/149 First World War Devastation near Fort Souville, Verdun Alamy 55/149 First World War Conscripts, among the first men ever to be compelled to join the British Army, undergo a medical Central Press/Getty Images 56/149 First World War Chandeliers and bed rest Getty Images 57/149 First World War The Pavilion was meant as a seaside home for the Prince Regent Royal Pavilion and Museums, Brighton & Hove 58/149 First World War Fun and games were vital Royal Pavilion and Museums, Brighton & Hove 59/149 First World War Patients get some sea air Royal Pavilion and Museums, Brighton & Hove 60/149 First World War The medical staff Royal Pavilion and Museums, Brighton & Hove 61/149 First World War Britain saw the Easter Rising as a stab in the back and the rebels, pictured here being led to captivity, as traitors. Subsequent executions made them into national heroes Rex 62/149 First World War A steamer hit by a torpedo during the First World War Getty 63/149 First World War The Ottoman army besieged the British forces for 147 days until they surrendered on 29 April 1916 Getty 64/149 First World War General Sir Charles Townshend 65/149 First World War The tear-stained letter Imperial War Museum 66/149 First World War Siegfried Sassoon as a second lieutenant in the Royal Welch Fusiliers. His bravery won him the Military Cross in July 1916, but he later turned against the war Getty Images 67/149 First World War The sinking of the ‘Queen Mary’ Getty Images 68/149 First World War Admiral John Jellicoe, commander of the British fleet Getty Images 69/149 First World War German destroyers off the English coast Getty Images 70/149 First World War One of the architects of the revolt: Sharif Hussain, religious leader of Mecca Getty Images 71/149 First World War One of the architects of the revolt: Sir Henry McMahon, British minister in Cairo Getty Images 72/149 First World War Emilio Lussu, who fought in the battle with the Italian Army, on the side of the allies, against the Austrians, who sided with Germany 73/149 First World War Field Marshal Horatio Herbert Kitchener, whose face appeared on the recruitment poster ‘Your Country Needs You’ Getty 74/149 First World War Conscientious objectors at a protest on Dartmoor in 1917 Getty 75/149 First World War Objectors were forced to cultivate the soil although many were said to have spent much of their time "strolling on the moors, reading, smoking and talking" Getty 76/149 First World War British conscientious objectors leaving Dartmoor Prison under a gateway inscribed with the words "Parcere subjectis" ("Spare the conquered") Getty 77/149 First World War Going over the top during the Battle of the Somme in 1916 PA 78/149 First World War The British Machine Gun Corps during the battle Hulton Archive/Getty Images 79/149 First World War Canadian troops prepare for the charge Hulton Archive/Getty Images 80/149 First World War Remains of the German airship shot down over Cuffley Popperfoto 81/149 First World War Captain William Leefe Robinson received the VC for his courage Hulton/Getty Images 82/149 First World War A British Mark 1 tank on the Western Front Topical Press/Hulton/Getty 83/149 First World War A British soldier covers a dead German on the firestep of a trench near the Somme Hulton/Getty Images 84/149 First World War Carnage on the road to Romania’s Turnu Rosu Pass. A German NCO stands beside an Italian-made cannon and the body of what may have been a gun crew member 85/149 First World War Edward Thomas, a Second-Lieutenant in the Royal Garrison Artillery, at home on leave in early 1917 Edward Thomas Fellowship 86/149 First World War Edward’s wife Helen with two of their three children, Merfyn and Bronwen 87/149 First World War May Bradford writing a letter for an injured soldier in a French hospital 88/149 First World War Composer and poet Ivor Gurney (left) and the artist Paul Nash Getty Images 89/149 First World War Filling shells at the Vickers munitions factory, Barrow-in-Furness. Strikers’ grievances included the use of female labour BAE Systems Submarines 90/149 First World War The moment that ushered in the American century: President Woodrow Wilson asks Congress to ratify a declaration of war against Imperial Germany AP 91/149 First World War Supporters greet Lenin on his arrival at Finland Station, Petrograd, on 16 April 1917, after a week-long journey by sealed train from Switzerland Everett Collection/Rex Images 92/149 First World War War effort: Women war workers at Cross Farm, Shackleton, Surrey, in 1917 Getty 93/149 First World War French ‘poilus’ at Chemin des Dames, where the bloody Nivelle Offensive of 1917 pushed many into mutiny Rex 94/149 First World War An early colour photograph of the crater left by the biggest of the blasts beneath German positions near Messines on 14 June 1917 Getty 95/149 First World War British sappers laying the mines Heritage Images/Getty 96/149 First World War The remains of a German trench Alamy 97/149 First World War Ernst Jünger’s German platoon overcame the enemy forces with his ‘mastery of the situation and iron command’ 98/149 First World War Siegfried Sassoon was sent to Craiglockhart Hospital to be treated for ‘shell shock’ following his protest Getty Images 99/149 First World War Erich Maria Remarque (1898-1970), whose 1929 novel, ‘All Quiet On The Western Front’, was based on his wartime experiences. Here he is seen with Carl Laemmle of Universal Pictures (left) Getty Images 100/149 First World War The conscription of reserve soldiers in Greece to fight on the Salonika front in 1916. The Greek city was ravaged by a fire the following year, which devastated the area and left thousands homeless Getty Images 101/149 First World War Allied troops marching down the Boulevard de la Victoire in Salonika in 1916, the year before the great fire which devastated the Greek city Getty Images 102/149 First World War Women leaving a munitions factory on Eiswerder Island in Spandau, near Berlin, at the end of their shift, in around 1917. They are crossing the bridge over the river Havel TopFoto 103/149 First World War Female workers of the Spandau factory getting their dinner during the midday break TopFoto 104/149 First World War Wet weather plagued the Third Battle of Ypres, which included the battles of Langemarck and Passchendaele. Perhaps 70,000 Allied soldiers died between 31 July and 10 November Getty 105/149 First World War A British stretcher party Getty 106/149 First World War German prisoners on a duckboard track at Yser Canal, Belgium, on the opening day of the battle Getty 107/149 First World War 3rd September 1917: Veterans of the American Civil War at the opening of the Eagle Hut Getty 108/149 First World War US Ambassador Page greeting veterans of the American Civil War at the opening of the Eagle Hut Getty 109/149 First World War 22nd December 1917: Christmas preparations at the Eagle Hut Getty 110/149 First World War Albin Köbis, who was shot as one of the ringleaders of the German naval mutiny in 1917 Alamy 111/149 First World War Stokers of the SMS Prinzregent Luitpold in 1913 Alamy 112/149 First World War Allied troops in what is now Zambia, in vain pursuit of the forces of the elusive German general Paul von Lettow-Vorbeck Getty Images 113/149 First World War Genius in the art of bush warfare: German general Paul von Lettow-Vorbeck Getty 114/149 First World War German women and children queue for food rations Alamy 115/149 First World War Crowds at Petrograd’s Winter Palace during the October Revolution. (Russia still used the Julian calendar, in which the West’s 7 November equated to 25 October) Getty 116/149 First World War The Mayor of Jerusalem (with walking-stick) had tried to surrender the city to them Imperial War Museum 117/149 First World War Allenby walks into Jerusalem: Sergeants James Sedgwick and Frederick Hurcomb of 2/19th Battalion, London Regiment, outside the city two days earlier AP 118/149 First World War Artist John Nash not only painted the ordeals of Britain’s front line troops: he experienced them first-hand 119/149 First World War A British housewife with her grocery items after the introduction of rationing. The government feared hunger might lead to revolution Rex 120/149 First World War Edmund Morel as an MP after his release Topham Picturepoint 121/149 First World War A suffragist rally in Hyde Park Hulton/Getty 122/149 First World War A newly enfranchised woman votes for the first time in 1918 Hulton/Getty 123/149 First World War Masked doctors and nurses treat flu patients lying on cots and in outdoor tents at a hospital camp during the influenza epidemic of 1918 Hulton Archive/Getty Images 124/149 First World War The immense long-range naval gun which was used to bombard Paris from behind the German lines in Picardy TopFoto 125/149 First World War The immense naval gun was manned by 80 German sailors. It launched its shells from behind the German lines TopFoto 126/149 First World War Walter Tull, left, Britain’s first black Army officer, in a photograph handed down to his great-nephew Edward Finlayson 127/149 First World War Tull was singled out for his "gallantry and coolness" following a daring raid across the frozen river Piave in January 1918 128/149 First World War The German air ace Baron Manfred von Richthofen Hulton/Getty 129/149 First World War Baron Manfred von Richthofen's 'flying circus' Hulton/Getty 130/149 First World War Dogs at the British War Dog School in Essex Mary Evans Picture Library 131/149 First World War Tweed, far left, with his handler Private Reid 132/149 First World War A dog courier runs through barbed wire and mines to deliver a message Corbis 133/149 First World War Piete Kuhr, pictured in 1915 Memoria Hürth 134/149 First World War Vera Brittain became a nurse during the war Hulton/Getty 135/149 First World War The aftermath of the explosion at the munitions plant in Chilwell Nottingham City Council 136/149 First World War Remains of a soldier on the Western Front, where millions were killed or wounded, or went missing Getty 137/149 First World War From left, Marshal Joffre, President Henri Poincaré, King George V, General Foch, and Field-Marshal Haig Time life pictures/Getty 138/149 First World War Captured German officers receiving orders from a French officer Universal Images Group/Getty Images 139/149 First World War American troops advance on a German position on the Saint Mihiel salient, north-eastern France, in 1918 140/149 First World War American soldiers of the 18th Infantry Machine Gun Battalion advance through the ruins of St Baussant on their way to the St. Mihiel Front Getty 141/149 First World War A group of captured Germans being marched through St Mihiel Salient Getty 142/149 First World War Wilfred Owen in uniform as a 2nd Lieutenant. The poet was teaching in France when the war began Fotosearch/Getty Images 143/149 First World War The poet Rainer Maria Rilke, circa 1920. The poet describes to his wife the rising tide of popular unrest in Munich Hulton/Getty 144/149 First World War The interior of the railway carriage in which the Armistice ending the First World War was signed Hulton/Getty 145/149 First World War The Allied delegation was led by France’s Marshal Ferdinand Foch (front row, second right) Getty Images 146/149 First World War The Royal Family appear on the balcony Getty Images 147/149 First World War People celebrate in the streets in 1918 Getty Images 148/149 First World War Crowds in London celebrate the end of hostilities on 11 November 1918 Getty Images 149/149 First World War Crowds in London celebrate the end of hostilities in 1918 Getty 1/149 First World War Supporting troops of the 1st Australian Division walking on a duckboard track near Hooge, in the Ypres Sector Getty Images 2/149 First World War Final moments: The Archduke of Austria Franz Ferdinand with his wife Sophie in Sarajevo minutes before his shooting AP 3/149 First World War Arresting Princip’s fellow conspirator Nedeljko Cabrinovic after a failed attempt to kill the Archduke on the same day Getty Images 4/149 First World War Crowds in central London cheer Britain’s declaration of war on Germany Getty Images 5/149 First World War The innocents: New recruits, with bicycles, training with the British Army in 1914 Getty 6/149 First World War 1914: A lone soldier with a bicycle stands amid the remains of a German motor convoy which lines a country lane after an attack by French field guns in the battle of the Aisne in France Topical Press Agency/Getty Images 7/149 First World War Troubled waters: The Cambridge eight included John Andrew Ritson (fourth from cox) Museum of London, Christina Broom 8/149 First World War John Andrew Ritson (left) Museum of London, Christina Broom 9/149 First World War Dennis Ivor Day Musuem of London; Christina Broom 10/149 First World War German infantry advance through Belgium in August 1914 Getty Images 11/149 First World War Civilians near the Austrian lines in Serbia are strung up – probably as a reprisal for guerrilla resistance to the invaders Miroslav Honzík/Hana Honzíková 12/149 First World War Captured soldiers of the Russian 2nd Army after their defeat at the Battle of Tannenberg Getty Images 13/149 First World War Wounded and exhausted British and Belgian soldiers retreating after the Battle of Mons Getty Images 14/149 First World War Crowds gather outside a recruitment office Getty Images 15/149 First World War French General Joseph Joffre (second right), Commander- in-Chief of the French Armies, and General Michel Joseph Maunoury (right) on the front during the First Battle of the Marne. Six hundred scarlet taxis were requisitioned, at a cost of Fr70,102, to ferry reservist troops to the Battle of the Marne in 1914 Getty Images 16/149 First World War A French firing squad escorts a deserter to his execution in November 1914 Getty 17/149 First World War One of the trenches from which deserters tried to escape Getty 18/149 First World War German soldiers in Wirballen, a border town between the German Reich and Russia Mary Evans Picture Library 19/149 First World War Carl Hans Lody, who spied in Britain Popperfoto/Getty 20/149 First World War Up to 12 million letters a week were sent to the front line via the wooden sorting office hastily set up in Regent’s Park in 1914 Royal Mail 21/149 First World War Survivors from SMS ‘Gneisenau’ in the sea off the Falkland Islands, with HMS ‘Inflexible’ in the background, 8 December 1914 Getty Images 22/149 First World War The ruins of the cloth hall and cathedral in Ypres during WWI Getty Images 23/149 First World War Margot Asquith, the Countess of Oxford and Asquith and the wife of Britain’s wartime leader Getty Images 24/149 First World War A wounded American in a London hospital reads a magazine with a red cross nurse by his bedside. A. R. Coster/Topical Press Agency/Getty Images 25/149 First World War A mass execution by firing squad following the unsuccessful Singapore mutiny of 1915 rebelsindia.com 26/149 First World War Indian soldiers serving in France were known for their fighting spirit Underwood Archives/Getty 27/149 First World War Russian artillery positions outside Przemysl, during the six-month siege of the heavily fortified Austro-Hungarian city, part of present-day Poland Hulton Archive/Getty Images 28/149 First World War Residents assess the damage after Suffolk was rocked by bomb attacks mounted by German Zeppelin Getty 29/149 First World War German infantrymen attack through a cloud of poison gas. By the end of the war, both sides had employed various kinds of gas Getty 30/149 First World War Children of Armenian refugees in a camp Getty 31/149 First World War Armenian civilians being led away by Ottoman soldiers 32/149 First World War A public hanging in Istanbul 33/149 First World War A pile of skulls from the Armenian village of Sheyxalan AFP/Getty 34/149 First World War Allied troops at Anzac Cove (Gaba Tepe) during the Gallipoli campaign Hulton Archive/Getty Images 35/149 First World War Allied troops unloading heavy guns in the Dardanelles Hulton Archive/Getty Images 36/149 First World War Volunteer nurse Florence Farmborough was part of the Russian retreat from Gorlice 37/149 First World War Cunard liner RMS Lusitania, after secret Whitehall misgivings about the official account of one of the most controversial and tragic episodes of the First World War were revealed in newly-released government documents. Almost 70 years after the Cunard liner RMS Lusitania was sunk by a German U-boat off the coast of Ireland, some officials expressed concern that the truth was still being covered up PA Wire 38/149 First World War The RMS Lusitania sailed from New York on 1 May 1915 on her last voyage; the liner was sunk off southern Ireland on 7 May Getty Images 39/149 First World War Welsh Liberal politician and future Prime Minister David Lloyd George (1863 - 1945) enjoys a quiet read of a newspaper in his garden with his faithful dog for company Getty 40/149 First World War French troops line up for inspection on a trench on the Western Front Getty Images 41/149 First World War German military prisoners, at Southend-on-Sea, on their way to Knockaloe Print Collector/Hulton Archive/Getty Images 42/149 First World War The railway line running the length of the access road into Knockaloe, the biggest camp in the British Isles 43/149 First World War Survivors of the sinking in Cobh, Co Cork Getty Images 44/149 First World War Robert Graves (1895-1985), who served on the Western Front from 1915 to 1917 45/149 First World War 2nd Lieutenant John Kipling is thought to have been killed in The Chalk Pit, in Loos, France, on 27 September 1915 Wikimedia Creative Commons 46/149 First World War Laid to rest: Edith Cavell circa 1905 Getty 47/149 First World War Her funeral cortege in London in May 1919 Getty 48/149 First World War George Samson is celebrated on a cigarette card of the time 49/149 First World War Flora Sandes, who rose from private to sergeant-major in the Serbian army, playing chess with her Serbian comrades. After the war ended, she was promoted to lieutenant 50/149 First World War Italian light infantry of the 1st Alpini Regiment on Monte Nero, during the Isonzo campaigns Universal History Archive/UIG/Getty Images 51/149 First World War As Italian as mozzarella cheese: Giuseppe Ungaretti 52/149 First World War French troops under shellfire during the Battle of Verdun Getty Images 53/149 First World War A French soldier is shot during a counter attack Alamy 54/149 First World War Devastation near Fort Souville, Verdun Alamy 55/149 First World War Conscripts, among the first men ever to be compelled to join the British Army, undergo a medical Central Press/Getty Images 56/149 First World War Chandeliers and bed rest Getty Images 57/149 First World War The Pavilion was meant as a seaside home for the Prince Regent Royal Pavilion and Museums, Brighton & Hove 58/149 First World War Fun and games were vital Royal Pavilion and Museums, Brighton & Hove 59/149 First World War Patients get some sea air Royal Pavilion and Museums, Brighton & Hove 60/149 First World War The medical staff Royal Pavilion and Museums, Brighton & Hove 61/149 First World War Britain saw the Easter Rising as a stab in the back and the rebels, pictured here being led to captivity, as traitors. Subsequent executions made them into national heroes Rex 62/149 First World War A steamer hit by a torpedo during the First World War Getty 63/149 First World War The Ottoman army besieged the British forces for 147 days until they surrendered on 29 April 1916 Getty 64/149 First World War General Sir Charles Townshend 65/149 First World War The tear-stained letter Imperial War Museum 66/149 First World War Siegfried Sassoon as a second lieutenant in the Royal Welch Fusiliers. His bravery won him the Military Cross in July 1916, but he later turned against the war Getty Images 67/149 First World War The sinking of the ‘Queen Mary’ Getty Images 68/149 First World War Admiral John Jellicoe, commander of the British fleet Getty Images 69/149 First World War German destroyers off the English coast Getty Images 70/149 First World War One of the architects of the revolt: Sharif Hussain, religious leader of Mecca Getty Images 71/149 First World War One of the architects of the revolt: Sir Henry McMahon, British minister in Cairo Getty Images 72/149 First World War Emilio Lussu, who fought in the battle with the Italian Army, on the side of the allies, against the Austrians, who sided with Germany 73/149 First World War Field Marshal Horatio Herbert Kitchener, whose face appeared on the recruitment poster ‘Your Country Needs You’ Getty 74/149 First World War Conscientious objectors at a protest on Dartmoor in 1917 Getty 75/149 First World War Objectors were forced to cultivate the soil although many were said to have spent much of their time "strolling on the moors, reading, smoking and talking" Getty 76/149 First World War British conscientious objectors leaving Dartmoor Prison under a gateway inscribed with the words "Parcere subjectis" ("Spare the conquered") Getty 77/149 First World War Going over the top during the Battle of the Somme in 1916 PA 78/149 First World War The British Machine Gun Corps during the battle Hulton Archive/Getty Images 79/149 First World War Canadian troops prepare for the charge Hulton Archive/Getty Images 80/149 First World War Remains of the German airship shot down over Cuffley Popperfoto 81/149 First World War Captain William Leefe Robinson received the VC for his courage Hulton/Getty Images 82/149 First World War A British Mark 1 tank on the Western Front Topical Press/Hulton/Getty 83/149 First World War A British soldier covers a dead German on the firestep of a trench near the Somme Hulton/Getty Images 84/149 First World War Carnage on the road to Romania’s Turnu Rosu Pass. A German NCO stands beside an Italian-made cannon and the body of what may have been a gun crew member 85/149 First World War Edward Thomas, a Second-Lieutenant in the Royal Garrison Artillery, at home on leave in early 1917 Edward Thomas Fellowship 86/149 First World War Edward’s wife Helen with two of their three children, Merfyn and Bronwen 87/149 First World War May Bradford writing a letter for an injured soldier in a French hospital 88/149 First World War Composer and poet Ivor Gurney (left) and the artist Paul Nash Getty Images 89/149 First World War Filling shells at the Vickers munitions factory, Barrow-in-Furness. Strikers’ grievances included the use of female labour BAE Systems Submarines 90/149 First World War The moment that ushered in the American century: President Woodrow Wilson asks Congress to ratify a declaration of war against Imperial Germany AP 91/149 First World War Supporters greet Lenin on his arrival at Finland Station, Petrograd, on 16 April 1917, after a week-long journey by sealed train from Switzerland Everett Collection/Rex Images 92/149 First World War War effort: Women war workers at Cross Farm, Shackleton, Surrey, in 1917 Getty 93/149 First World War French ‘poilus’ at Chemin des Dames, where the bloody Nivelle Offensive of 1917 pushed many into mutiny Rex 94/149 First World War An early colour photograph of the crater left by the biggest of the blasts beneath German positions near Messines on 14 June 1917 Getty 95/149 First World War British sappers laying the mines Heritage Images/Getty 96/149 First World War The remains of a German trench Alamy 97/149 First World War Ernst Jünger’s German platoon overcame the enemy forces with his ‘mastery of the situation and iron command’ 98/149 First World War Siegfried Sassoon was sent to Craiglockhart Hospital to be treated for ‘shell shock’ following his protest Getty Images 99/149 First World War Erich Maria Remarque (1898-1970), whose 1929 novel, ‘All Quiet On The Western Front’, was based on his wartime experiences. Here he is seen with Carl Laemmle of Universal Pictures (left) Getty Images 100/149 First World War The conscription of reserve soldiers in Greece to fight on the Salonika front in 1916. The Greek city was ravaged by a fire the following year, which devastated the area and left thousands homeless Getty Images 101/149 First World War Allied troops marching down the Boulevard de la Victoire in Salonika in 1916, the year before the great fire which devastated the Greek city Getty Images 102/149 First World War Women leaving a munitions factory on Eiswerder Island in Spandau, near Berlin, at the end of their shift, in around 1917. They are crossing the bridge over the river Havel TopFoto 103/149 First World War Female workers of the Spandau factory getting their dinner during the midday break TopFoto 104/149 First World War Wet weather plagued the Third Battle of Ypres, which included the battles of Langemarck and Passchendaele. Perhaps 70,000 Allied soldiers died between 31 July and 10 November Getty 105/149 First World War A British stretcher party Getty 106/149 First World War German prisoners on a duckboard track at Yser Canal, Belgium, on the opening day of the battle Getty 107/149 First World War 3rd September 1917: Veterans of the American Civil War at the opening of the Eagle Hut Getty 108/149 First World War US Ambassador Page greeting veterans of the American Civil War at the opening of the Eagle Hut Getty 109/149 First World War 22nd December 1917: Christmas preparations at the Eagle Hut Getty 110/149 First World War Albin Köbis, who was shot as one of the ringleaders of the German naval mutiny in 1917 Alamy 111/149 First World War Stokers of the SMS Prinzregent Luitpold in 1913 Alamy 112/149 First World War Allied troops in what is now Zambia, in vain pursuit of the forces of the elusive German general Paul von Lettow-Vorbeck Getty Images 113/149 First World War Genius in the art of bush warfare: German general Paul von Lettow-Vorbeck Getty 114/149 First World War German women and children queue for food rations Alamy 115/149 First World War Crowds at Petrograd’s Winter Palace during the October Revolution. (Russia still used the Julian calendar, in which the West’s 7 November equated to 25 October) Getty 116/149 First World War The Mayor of Jerusalem (with walking-stick) had tried to surrender the city to them Imperial War Museum 117/149 First World War Allenby walks into Jerusalem: Sergeants James Sedgwick and Frederick Hurcomb of 2/19th Battalion, London Regiment, outside the city two days earlier AP 118/149 First World War Artist John Nash not only painted the ordeals of Britain’s front line troops: he experienced them first-hand 119/149 First World War A British housewife with her grocery items after the introduction of rationing. The government feared hunger might lead to revolution Rex 120/149 First World War Edmund Morel as an MP after his release Topham Picturepoint 121/149 First World War A suffragist rally in Hyde Park Hulton/Getty 122/149 First World War A newly enfranchised woman votes for the first time in 1918 Hulton/Getty 123/149 First World War Masked doctors and nurses treat flu patients lying on cots and in outdoor tents at a hospital camp during the influenza epidemic of 1918 Hulton Archive/Getty Images 124/149 First World War The immense long-range naval gun which was used to bombard Paris from behind the German lines in Picardy TopFoto 125/149 First World War The immense naval gun was manned by 80 German sailors. It launched its shells from behind the German lines TopFoto 126/149 First World War Walter Tull, left, Britain’s first black Army officer, in a photograph handed down to his great-nephew Edward Finlayson 127/149 First World War Tull was singled out for his "gallantry and coolness" following a daring raid across the frozen river Piave in January 1918 128/149 First World War The German air ace Baron Manfred von Richthofen Hulton/Getty 129/149 First World War Baron Manfred von Richthofen's 'flying circus' Hulton/Getty 130/149 First World War Dogs at the British War Dog School in Essex Mary Evans Picture Library 131/149 First World War Tweed, far left, with his handler Private Reid 132/149 First World War A dog courier runs through barbed wire and mines to deliver a message Corbis 133/149 First World War Piete Kuhr, pictured in 1915 Memoria Hürth 134/149 First World War Vera Brittain became a nurse during the war Hulton/Getty 135/149 First World War The aftermath of the explosion at the munitions plant in Chilwell Nottingham City Council 136/149 First World War Remains of a soldier on the Western Front, where millions were killed or wounded, or went missing Getty 137/149 First World War From left, Marshal Joffre, President Henri Poincaré, King George V, General Foch, and Field-Marshal Haig Time life pictures/Getty 138/149 First World War Captured German officers receiving orders from a French officer Universal Images Group/Getty Images 139/149 First World War American troops advance on a German position on the Saint Mihiel salient, north-eastern France, in 1918 140/149 First World War American soldiers of the 18th Infantry Machine Gun Battalion advance through the ruins of St Baussant on their way to the St. Mihiel Front Getty 141/149 First World War A group of captured Germans being marched through St Mihiel Salient Getty 142/149 First World War Wilfred Owen in uniform as a 2nd Lieutenant. The poet was teaching in France when the war began Fotosearch/Getty Images 143/149 First World War The poet Rainer Maria Rilke, circa 1920. The poet describes to his wife the rising tide of popular unrest in Munich Hulton/Getty 144/149 First World War The interior of the railway carriage in which the Armistice ending the First World War was signed Hulton/Getty 145/149 First World War The Allied delegation was led by France’s Marshal Ferdinand Foch (front row, second right) Getty Images 146/149 First World War The Royal Family appear on the balcony Getty Images 147/149 First World War People celebrate in the streets in 1918 Getty Images 148/149 First World War Crowds in London celebrate the end of hostilities on 11 November 1918 Getty Images 149/149 First World War Crowds in London celebrate the end of hostilities in 1918 Getty

Organisers have hailed Lights Out it as “one of the most dramatic UK-wide events ever organised”, where people will join a “shared moment of reflection” to commemorate the start of one of the darkest periods in our history.

It is one of many events taking place today marking the centenary of Britain’s involvement in the First World War, including services at Glasgow Cathedral and at the Commonwealth War Graves Commission cemetery in Mons, Belgium.

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David Cameron said: “A hundred years ago today Britain entered the First World War and we are marking that centenary to honour those who served, to remember those who died, and to ensure that the lessons learnt live with us forever.

“It is right to remember the extraordinary sacrifice of a generation and we are all indebted to them because their most enduring legacy is our liberty.”

Germany declared war on France and invaded Belgium on 3 August 1914 and when the country ignored Britain’s ultimatum to withdraw by the end of the following day, the Government declared war.

More than 9 million soldiers were killed in the ensuring conflict, including around 800,000 British soldiers and more than 120,000 civilians who died as a result of military action, malnutrition and disease.