A year ago this month, the haunting faces of unknown British and Commonwealth soldiers of the Somme emerged from the mists of time and battle to gaze from the pages of The Independent Magazine. The lost Somme photographs – 400 glass negatives of Tommies, Aussies and Canadians of the period 1915-16 rescued from a rubbish heap in northern France – generated extraordinary interest all over the world. The images were by far the most visited item on The Independent website in 2009 – and over the past 12 months, these "unknown soldiers" have been viewed online more than 1,700,000 times.

France's First World War graveyards, and the many "memorials to the missing", contain a legion of names without faces. By contrast, the Somme photographs presented us with scores of faces without names.

The Independent article was followed up by local newspapers and television channels in France. As a result, people in the Somme département have now come forward with more old photographic plates, this time mostly of Scottish and English Tommies. A selection of these new images is published here for the first time: a second "lost platoon" of nameless British soldiers snapped as individuals, or in groups, by an unknown French photographer. Hundreds of other images have been located and are awaiting collection, scanning and processing.

All the images – the 40-odd new discoveries and the original 400 – can be seen here. The new exclusive images can be launched from the photograph above and the original 400 are at Exclusive: The unseen photographs that throw new light on the First World War. They present a poignant snapshot of the British and Empire army on the eve of, or during, the horrific Somme conflict of July-November 1916. The pictures capture an army at a time of transition. The regular and territorial soldiers, who fought in the terrible battles of 1914 and 1915, have almost all vanished. They have been replaced by Lord Kitchener's amateur volunteers – the "Pals" and "Chums" – who fought for the first time, and died in their tens of thousands, in the Somme offensive.

There are one or two hatched-faced, walrus-moustached soldiers of the old school with faces that could have fitted into the ranks at Inkerman or Waterloo. But the great majority of the soldiers seem heart-wrenchingly young and startlingly modern. They look like the kind of people you could meet on the street, or in a pub, in 2010.

Look at the two teenaged first lieutenants – "warts" to the older officers – who pose self-consciously with their cigarettes (above). They can be scarcely more than 18, and probably straight from public school. Look at the young Scotsman, little more than a boy, with a pistol several sizes too big for him (maybe a German "souvenir"). Look at the kilted Scottish soldiers, jauntily wearing their gas-mask holders where their sporrans should be.

Michael Stedman, a historian of the 1914-18 war and an expert on the Somme, believes the new images come from a slightly later period than the first batch published here last year: possibly from towards the end of the battle in October-November 1916.

"This is suggested by the presence of troops from the Royal Naval Division, which was not in the area until October onwards," he said. "Underfoot conditions look wet which would support this thesis of the images being taken during October-December 1916.

"There are men from the Machine Gun Corps and many other Corps and units, often mixed together... I suspect there is a medical unit present in the area and many of these men may be recovering from light wounds – but that is only conjecture. That idea seems to be supported by the complete absence of 'kit', apart from the rather odd posed image of the Scots private with a possibly non-standard pistol and holster which looks very strange – possibly captured."

The historical value of the plates, as a record of the British army during the most murderous battle in its history, was first grasped by two local men: Bernard Gardin, a photography enthusiast, and Dominique Zanardi, proprietor of the "Tommy" café in Pozières in the heart of the Somme battlefields.

A local amateur photographer is believed to have taken the first pictures between the autumn of 1915, after the British army relieved the French on the Somme, and the autumn of 1916, when the "Big Push" ended in a muddy, and bloody, stalemate. The unknown photographer presumably made a little money by charging British, Australian and Canadian soldiers a few francs for a snap which they could send home to their loved ones.

The original cache of photographs, preserved on 9x12cm glass plates, lay undisturbed for nine decades in the attic of a ramshackle barn at Warloy-Baillon, 10 miles behind the battlelines of 1916. When the barn was restored in 2007, the photographic plates were thrown into a rubbish skip. Passers-by rescued some of them. Others were lost – until now.

In 2008, Gardin, a 62-year-old amateur photographic historian, was given a batch of 270 glass plates by someone who knew of his hobby. He approached 49-year-old Zanardi, who has a museum and a collection of First World War memorabilia at his café. (His most recent acquisitions include several packets of perfectly preserved, army-issue oatmeal biscuits, with an eat-by date of 1917, also found in a Somme barn. I heroically tasted one. What does a 94-year-old British military biscuit taste of? Nothing.)

When Gardin approached him in 2008, Zanardi already had 130 similar photographic plates which he had been given by other local people. The two men, at their own expense, scanned and digitalised and, in some cases, lovingly restored the combined batch of 400 images.

Exactly the same procedures have now been applied to the new plates which were offered up by local people after The Independent and subsequent French media stories. The donors told Zanardi that they had bought the plates at local car-boot and jumble sales in the last couple of years. Up to another 500 or so images are waiting to be collected and processed.

Gardin believes that the new batch, shown here, may be the work of the same unknown local photographer as the first collection published by The Independent Magazine a year ago. Zanardi, however, is convinced that they were taken by another photographer. "The backgrounds are different and, to me, the style is different," he told me.

Between them, the two men have combed the area around Warloy-Baillon, looking for the buildings glimpsed in the backgrounds of the images in the hope of tracing the photographer's descendents. "We have got nowhere," Zanardi reported. "That area was largely destroyed in the later battles of spring 1918. The buildings have probably vanished."

Are the two men surprised at the extraordinary interest that their work has provoked all around the globe? "I have been following the debate on The Independent website," Gardin said. "Here in the Somme, people have a sense of duty to remember the soldiers who came from so far to fight for France. It has been very moving to find that the same interest survives in the countries from which the soldiers came."

Last year, The Independent appealed for information from anyone who thought that they might be able to identify a relative in the first batch of images. After 93 years, that was the longest of long shots. All the same, two or three tentative identifications were made and there was one near-certain match.

A young artilleryman sitting on the far left of the front row of the group of gunners in one photograph has been positively identified by family members as Jim Mundell from Dumfriesshire, who arrived on the Somme with the Royal Regiment of Artillery in September 1916. He was 20 at the time. He survived the war to become a farmer and died in 1955.

The original Somme photographs attracted – and continue to attract – scores of comments from The Independent website readers from all over the world. They have generated two poems and an impolite argument over whether Sir Douglas Haig, the commander of the British armies on the Western Front from December 1915 to November 1918, should still be honoured by an equestrian statue in Whitehall.

For many internauts, it was the sheer ordinariness of the soldiers – not posed stiffly, or lit heroically like many similar portraits taken in Britain – which was so compelling. "Countup" wrote: "I know them all. I can put the face of a friend, colleague, family member or person in our street in to almost any photo and they would not look out of place. Time distorts the horror of WWI but they are all just ordinary people like you."

Michael Stedman, the Somme historian, thinks that, overall, the two sets of images are a mix of medical orderlies, soldiers possibly recovering from light wounds and soldiers about to enter the slaughter a few miles to the east. Warloy-Baillon was the site of a clearance hospital, where troops were treated before being sent to Britain – or back into the line.

Mr Stedman said: "Prints from these plates would have been sent home to loved ones as a way of saying, 'Here, look at me, I am in France and I'm doing fine'."

The Somme was the most murderous single battle of the 1914-18 war. In a little less than five months, an estimated 1,000,000 British Empire, French and German soldiers were killed, captured or wounded. There were more than 400,000 British and Empire casualties, including 125,000 deaths – 27,000 on the first day alone.

For how long the nameless soldiers shown here were "doing fine" we may never know.

* If you have any information about the soldiers in the photographs, or about the identity of the photographer, please e-mail magazine@independent.co.uk