At Loos in Northern France, the excavation you and your team worked on was interfered with by looters. How did this affect your ability to identify the soldiers from that site?

Any interference with a site has the potential to damage evidence because there is no record of what was removed or disturbed. If human remains are damaged by looters it is because they were looking for metal items such as badges - the very item we would use to help establish identification. The result is that in the worst possible case all that is left is a mass of bones dug out of the ground and discarded. Sadly I was one given such a bag of bones by a French land-owner whose site had been targeted. Although I handed the remains to the Commonwealth War Graves Commission it was impossible to tell the man’s nationality still less his unit or name. He was one of the missing that self interest had ensured would be forever ‘Known Only Unto God’.

The battle fields across Belgium and Northern France are still scattered with the fragments of war such as ammunition. How do you keep your sites safe and do you have bomb experts on hand to remove live ammunition?

On all the sites we work under the supervision of a military or civilian Explosive Ordnance Disposal (EOD) expert. He is the person who briefs all the participants in what to look out for and is called immediately if an archaeologist finds anything suspicious. This results in frequent delays, but safety is vitally important and the grenade or shell we find is potentially just as dangerous as when it was first fired. A greater threat is chemical weapons such as gas. This type of weapon is often in a thin metal container and may be leaking when discovered. As a result the archaeological site is decorated with fluttering pieces of orange tape tied to posts, fences and trees. In the event of gas or any odd chemical smell being detected on the shout ‘Gas, Gas, Gas’ (the same called was used in the Great War) the team retires up wind to await the EOD experts opinion. On one occasion this turned out to be the smell from a 90-year-old latrine bucket.

As well as being an expert historian for the National Army Museum in London, you are also a member of No Man's Land, can you tell us more about this organisation and how you got involved with them?

About 15 years ago I visited the Somme with two friends. One, Jon Price, is an archaeologist and the other, Alastair Fraser, an historian. By chance we stayed in a guesthouse belonging to Avril Williams in the village of Auchonvillers (Ocean Villas to British troops). She showed us her cellar that was used as a dug out during the war. She also explained that she believed that traces of a connecting trench system could be found in her garden. Jon offered to return that Autumn to dig a cross section of the trench. Ten years later we were still tracing the trenches in Avril’s garden. However in 2003 the team was given the opportunity to extend out work when the BBC asked us to look for the location of the dugout occupied by Wilfred Owen in January 1917 and about which he wrote the poem ‘The Sentry’. We failed to find the dugout, but located a German trench system and three sets of human remains. Two turned out to be Germans killed in June 1915 and the other British who died on 1st July 1916.

Where does your interest in battlefield archaeology stem from?

It is an odd thing that I never wanted to be a soldier - too dangerous, wet and cold - but was always fascinated by military history. At school I became a member of the War Games club and later joined an English Civil War re-enactment group. Having studied History at University I became a teacher and within a few years joined the staff at the National Army Museum. Here I was able to research battlefields and study the uniform and equipment of the British soldier over the past 500 years. As a result I was asked to take part in the television series ‘Two Men in a Trench’ as the military expert. Twelve battlefields and hundreds of artefacts later I was still fascinated and only making a few mistakes. I still have much to learn, but my fascination with the Great War is still there.

The National Army Museum covers military history from across the ages, what is your preferred military age and why?

The National Army Museum covers the period from Agincourt in 1914 through to the present day. Although I started at the Museum as a specialist on the English Civil Wars the last ten years of archaeology and research means I can claim to have a well developed interest in the Great War, specifically the Somme.

Andy Robertshaw's book on the first day of the battle, The Somme 1st July 1916: Tragedy and Triumph, was launched on the Somme in July 2006.