Four years ago, construction workers clearing the land for a new hospital in northern France made a grim discovery.

Soon after, they had unearthed the remains of more than 100 people.

Such finds are not unusual in this part of France and the police knew exactly who to call.

Stephan Naji, the head of the recovery unit from the Commonwealth War Graves Commission (CWGC), arrived on the scene within hours.

It was the start of a painstaking investigation which eventually solved a 100-year-old mystery by identifying two missing Scottish soldiers.

Stephan runs a team of specialist archaeologists who are on standby 24/7.

Once they confirm that soldiers' bodies have been found they remove the remains and any artefacts and extract as much information as possible.

The building site at Lens had been on the Western Front during World War One and was the scene of the Battle of Loos, one of the biggest in the conflict.

At the commission's headquarters near Arras, Stephan showed us trays of objects which had been found there, including parts of boots, rusted belt buckles, shoulder badges, buttons and regimental insignia.

Stephan's team analysed everything that was found.

Thousands of soldiers are still missing in action in the area, and the discovery of items from individual regiments enabled them to narrow down who the individuals might be.

Shoulder badges indicated that the remains could include soldiers who had fought for two Scottish regiments - the Gordon Highlanders and the Cameron Highlanders.

But to establish who they were it was time to pass the case on to another specialist unit based in the UK.

A nondescript office block at the far end of the Imjin barracks in Gloucester is home to a small Ministry of Defence unit called the Joint Casualty and Compassionate Centre (JCCC).

The team is tasked with identifying British troops who were killed in historical campaigns.

Not many know about their work, but those who do have nicknamed them the war detectives.

Nicola Nash has been a case worker at the JCCC for 10 years.

In 2023, she was told about the remains which had been found in France two years earlier.

After looking at the list of the Cameron Highlander soldiers who were still missing from the Battle of Loos, Nicola narrowed the search to........

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