On 4 August everyone in the UK – and internationally – is being urged to turn their lights out to mark 100 years since Britain announced war on Germany.

At a press conference on 10 July, in the very building where the Foreign Secretary, Sir Edward Grey, uttered the immortal words: “The lamps are going out all over Europe; we shall not see them lit again in our lifetime,” the former MP’s great, great nephew, Adrian Graves, urged Britons to get behind a poignant project to see all the LIGHTS OUT from 10pm-11pm tonight (4 August), 100 years since Britain joined the First World War.

At 11pm on 4 August 1914 Britain officially declared war on Germany, but it wasn’t until his memoir was published in 1925 that Grey’s conversation with his friend, John Spencer, on 3 August 1914 in which he said the memorable sentence, became public knowledge.

Graves said his great, great uncle was really anti war and after delivering a speech in the House of Commons on 3 August in which he effectively committed the nation to a war in Continental Europe, he returned to his office, banged the table and said: “I hate war, I hate war, I hate war.”

Graves said: ” My great, great uncle, Sir Edward Grey was central to the events that took place 100 years ago. It’s wonderful to be near the actual room where we are told he said the actual words.”

As part of the 14-18 NOW WWI Centenary Art Commissions, which will mark significant dates between now and Armistice Day 2018 with a series of art projects, the nation will be asked to join in a symbolic turning out of the lamps by extinguishing all the lights in their home, with the exception of a single candle left burning.

There will also be a number of public events to coincide with the official candle vigil at Westminster Abbey and landmarks such as the Houses of Parliament, the Imperial War Museum, Blackpool Illuminations, Tower Bridge and the Eden Project will all be turning their lights out.

In addition, international audiences will be asked to join in by turning out their lights between 10pm-11pm local time, and a photo of a candle will be tweeted by the Foreign Office, which it hopes will be sent across the world digitally.

Vikki Heywood, chair of the 14-18 NOW project, said: “Lights Out has the opportunity – I think – to be a major national moment of reflection across generations.”

Spread the word about this momentous occasion by tweeting #LightsOut