What started as a boyhood summer holiday adventure has become a fascinating glimpse into history for a group of north Norfolk teenagers who are restoring a Second World War pillbox.

Jake Brader, 16, and his friends have discovered wartime graffiti, wall paintings - and unexploded hand grenades which had to be detonated by the bomb squad.

They first tracked down the hidden pillbox three years ago with a vague idea of turning it into a den.

The landowner has asked that its precise north Norfolk location is not identified.

Last summer Jake, of High Street, Sheringham, Connor Savage, 17, of Northmead Drive, North Walsham, Jared Herring, 16, of Bradmoor Road, Felmingham, and Kieran Etherington, 16, of Patch Meadow, North Walsham, spent two days pulling off the ivy strangling and hiding the structure and began to explore its interior.

Scribbled on the walls were scarcely-legible names of wartime soldiers, dates, and their army numbers.

Jake managed to decipher one name – Pte R Pearce – pencilled with his military number and the date June 20 1940.

That month saw the fall of France to the Nazis and Hitler then turned his attention to his next invasion target – Britain.

The pillbox formed part of the East coast's line of defence, with Weybourne known to be a possible landing place for the Germans.

Jake's research has revealed that Roy Leonard Nelson Pearce came from Metfield, in Suffolk, and he was in the 6th Royal Norfolks.

Pte Pearce served in the Far East and was killed, aged just 23, on January 27 1942. His name is recorded on the Singapore memorial at Kranji.

A few metres from the pillbox the teens came across another wartime building which Jake believes is an 'elephant hut', used by soldiers or the Home Guard to rest between shifts in the pillbox.

Painted on its inside walls were the words 'Eagle' with the flaky remains of an eagle's head, plus crossed flags and symbols.

Outside, the blast wall - which protected the entrance from a grenade being thrown into the hut – is intact but lying on the floor.

In the surrounding woodland the quartet stumbled on an ammunition dump containing four hand grenades which were detonated by the military earlier this month. They have also uncovered a network of trenches in the area.

Jake, who is studying history as one of his A-level choices at Paston College in North Walsham, said the discoveries had been exciting and interesting.

'It's strange to find out about someone 70 years ago in the modern era,' he said. 'It drives you on to do more. I think it's an under-exposed part of our history. We want to carry on elsewhere, with other pillboxes.'