The relatives of two million soldiers who served in the trenches of the Great War are to be allowed to read their once-secret war records, nearly 85 years after the conflict ended.

The vast archive, which is held at the Public Record Office in Kew, south-west London, contains nearly 24 million pages of documents, including the soldiers' once confidential medical, disciplinary and war records and private letters.

In some cases, relatives who have read the first batches of released papers have had some startling surprises, such as discovering that their men had children from previous marriages or had concealed having caught sexually transmitted diseases on duty.

And buried among the documents are the tattered records of the author and satirist "Saki" – H H Munro – who was killed in the trenches on 14 November 1916. They record that Munro had been hospitalised with influenza and then promoted to lance-sergeant in the weeks before he died.

The completion of the archive, which is announced by the PRO today to mark Remembrance Sunday, has delighted historians and socio- logists. Until now, only officers' and Guards regiments' records had been widely available to the public and historians. The new archive, which includes only privates and non-commissioned officers, is now one of the largest and most detailed surviving records of military life and British society during the Edwardian era.

These documents had lain largely unread for 55 years after surviving the Blitz. In September 1940, in the earliest days of the Blitz, a Luftwaffe incendiary bomb deva- stated the War Office's vast records store in Bermondsey, south London.

The store had held more than 6.5 million service records from the late 1890s through to 1920. Only two million individual records survived the blast and subsequent fire. They were left in a delicate condition and became known to historians as the "burnt documents".

Archivists have spent nearly seven years copying the singed and fragile pages on to microfilm, after being given £5.3m from the Heritage Lottery Fund and the Mormon Genealogical Society of Utah, which places great religious weight on tracing family lines.

The papers also include much clearer evidence about the tens of thousands of Asian, African-Caribbean, Canadian, Australasian and even Armenian men who volunteered, said William Spencer, a PRO historian. "It is now possible to study the final part of the world war – the human dimension," he said. "It contains two million individual stories, and their personal circumstances. It's fascinating."

Hew Strachan, professor of the history of war at Oxford University and an expert on the Great War, said that the "burnt documents" would shed light on the migration, employment, and living patterns over 20 years of British social history.

They would allow academics to answer controversial questions about the mental and physical fitness of recruits. "These are extraordinarily detailed and informative," he said. "The questions that leap to mind are: is it true that medical standards were waived when manpower quotas were getting desperate? Is it true that there was no real psychological profiling for those accused of cowardice?"

* A campaign to raise £1.2m for Britain's first national memorial to the hundreds of thousands of animals that died or saw active service was boosted last night by a £25,000 donation from the Amalgamation of Racing Pigeons group. The memorial is to be built on London's Park Lane.

The boy from Moss Side
Every woman in the Cookson family has a portrait of Joe Cookson on the wall, in honour of the teenaged soldier who lied about his age to join up, and never came home.

Adding months to his age, he claimed to be 17 and answered one of General Kitchener's first calls to arms, joining the 12th Battalion, the Manchester Regiment in October 1914.

Joe, from Moss Side, Manchester, died on the Western Front in the winter of 1915, leaving behind a few personal effects, his military portrait and a mystery: how and when exactly did he die?

His great-niece, Lynne Cookson, has now found his service record in the Public Record Office, which answers a few questions. It reveals that he served for only a few weeks at the front before he was killed. And in those documents is a short, tattered letter from his parents, anxiously asking the War Office to confirm an eyewitness report from one of his comrades that their son had died.

Joe's sister Ada, now in her 90s, has seen the letter. "It did bring him back, and she started talking about him more," said Lynne Cookson. "When I first read their letter I was actually quite angry they had to write and ask what had happened to their son. I can't imagine how my great-grandparents felt."

A rough diamond redeemed
Private Jack Sweeney is well known to military historians as the rough diamond who exchanged gentle love letters from the trenches with Ivy, a Sunday school teacher in suburban London.

But the romantic story has been given a fresh twist by the discovery in his service records of a long series of disciplinary offences, which he kept quiet from Ivy and their children.

The papers show that while serving as a cook on the Somme, at Ypres and in the Mediterranean, he was repeatedly put on charges and confined to barracks. Among other offences, he went absent without leave, hit a sergeant in Gibraltar and got drunk in Marrakesh. He served 165 hours' detention for being insubordinate to an NCO, was confined to barracks for seven days for neglecting his rifle and for a further 14 days for insulting another NCO.

These revelations suggest that Jack Sweeney was redeemed by his long-distance affair with Ivy, said Malcolm Brown, an Imperial War Museum historian who first uncovered the story.

"He was a real skiver and scrimshanker, saved by the love of a wonderful woman," he said. They married in March 1918, and lived together happily until Jack's death in 1960.