OXFORD archaeologists yesterday began excavating the biggest Great War mass grave discovered in decades.

Up to 400 First World War soldiers from Britain and Australia are thought to lie in eight pits in the French countryside.

Staff from Oxford Archaeology, in Osney Mead, will exhume the bodies on behalf of the British and Australian governments, supervised by the Commonwealth War Graves Commission, which is building a new cemetery for the dead.

The operation in Pheasant Wood, near the village of Fromelles about seven miles south of the French-Belgian border, is expected to last until the end of September.

In May last year, a limited excavation revealed pits which had remained untouched since the Battle of Fromelles, more than 90 years ago.

The hope is to use DNA testing to identify as many of the bodies as possible.

The main British units involved in the battle included the 2/4th Territorial Army Battalion of the Oxfordshire & Buckinghamshire Light Infantry, and battalions from the Gloucestershire Regiment and the Royal Warwickshire Regiment.

Earlier this year, John Blakeman, the war memorial co-ordinator for the Oxfordshire Family History Society, said he thought it unlikely that soldiers from the Oxford area had died at Fromelles.

Next year, the bodies will be laid to rest in individual graves at the new cemetery — the first war cemetery the commission has built in almost 50 years.

The Battle of Fromelles, which began on July 19, 1916, was the first major battle on the Western Front involving Australian troops.

It proved costly for the Allies. Records suggest that between July 19 and 21 the Australian dead at Fromelles amounted to 1,780 men, along with thousands more soldiers who were wounded, while the British units lost 503 dead.