A rusty U-boat gun which spent more than 80 years under the Channel has been branded unsafe by police.

The historic gun has been on display outside Newhaven Maritime Museum since 2001.

Sussex Police have insisted the gun must have either a firearm certificate or a certificate of decommissioning to show it cannot be fired.

Museum curator Pete Bailey said a decommissioning certificate was on its way and there was no way the gun could be used.

He said: "It has really been taking things a bit too far and was a rather over the top reaction.

"The gun has been here for four years and after all that time in the mud before there was no way it could be used. If anyone did try to use it they would end up damaging themselves more than anything else.

"What on earth would we want a firearms certificate for?

"We are now waiting for the certificate declaring it is unusable and we will have something riveted on to the gun saying this.

"Anyone who knows anything about guns will know that to fire it the barrel needs to be clear. After all those years in the water this gun is blocked with all types of things.

"They came to have a look at it before the Labour Party conference in Brighton and that was when they said it needed a certificate.

"I know they were a bit jittery before the conference but it is so obvious the gun cannot be used. I would have thought the police would have had more important things to be focusing on."

The gun was salvaged by divers from Tunbridge Wells who discovered the wreck of the German submarine off Beachy Head. The 16ft-long one-tonne weapons barrel is blocked with mud, shale and a metal stopper.

U-130 put to sea just a few days before the end of World War I and never fired a shot.

It was being towed to a scrapyard in 1920 when it broke free and sank in the Channel.

Sussex Police said that under the Firearms Act 1968 the U-boat gun was classed as a firearm and needed a certificate, which was why the museum had been sent a letter to remind them of their obligations under the law.