Hundreds of people were forced to flee when a man walked into a theatre carrying a live mortar bomb and said: "What should I do with this?"

Moments earlier he had found the device - believed to be a remnant of the preparations for D-Day in 1944 - sticking out of the sand on Littlehampton's main holiday beach, near Harbour Park leisure complex.

He scuffed the mortar free of sand with his foot, picked it up and carried it into the Windmill Theatre, where adult members of the 1st Rustington Scout group were preparing for a dress rehearsal.

Anne Lecuyer, producer of the show, which runs from Thursday to Saturday, said: "This bloke walked into the theatre holding it in his hand and said: "What should I do with this?"

"We told him to put it down and then called the police. He had his wife and 12-year-old kid with him at the time.

"He had scuffed it out of the sand with his boot and seemed very nonchalant about it."

With 70 Cubs in uniform due to turn up for a full dress rehearsal, police cleared the theatre and neighbouring Harbour Park and threw a cordon around the area. No houses were evacuated.

While Army bomb disposal experts from Aldershot examined the device, which was taken outside and placed near public toilets, the Cubs sang We're Riding Along On The Crest Of A Wave at a safe distance.

The mortar was surrounded by sandbags and the fuse blown up to make it safe before the all-clear was sounded several hours later.

Anne added: "There was a small noise at first but the second time it was a huge explosion. All the Scouts watched and it was quite exciting but we were two hours late with our dress rehearsal."

During the Second World War the Littlehampton area was turned into an Army training area in the run up to D-Day in 1944 and the seabed is littered with ordnance, which is occasionally washed up on the beach.

Members of the Royal Logistics Corps in Aldershot, who carried out the controlled explosion, said this was unusually dangerous, however.

A spokesman for the 11 Explosive Ordnance Disposal regiment said: "This was a two-inch mortar high explosive.

"These were used from the Thirties until fairly recently but probably came from the preparation for D-Day.

"Two-inch mortars are quite common but high explosives are rare and dangerous.

"The bottom line is if anything is considered dangerous, people should call the police who will inform us.

"It is not worth risking lives for."

A police spokesman urged people not to pick up munitions found on the beach but to leave them alone and dial 999.

Radio stations had been asked to warn residents that the explosion was about to take place.