The trawler Lunar B dredged up the mine off the Dengie Flats near Colchester in north Essex on Thursday morning.

A team of Royal Navy divers was sent from Portsmouth to an area just off the River Blackwell to examine the explosive.

During low tide, members of the bomb disposal squad carried out a controlled explosion to make the device safe.

A Royal Navy spokesman said the explosive was the largest and deadliest type of mine the bomb disposal teams were asked to deal with.

Well preserved

"The GC mine is the biggest and most powerful mine used in the war and was designed to break the backs of ships," he said.

"They are usually quite well preserved as they are encased in stainless steel."

A one mile exclusion zone was put in place around the mine to prevent any ships straying into the area.

A disposal team from Portsmouth was also called to Norfolk on Wednesday after a dredger discovered a suspected bomb near Sea Palling.