Chris Hovard, 51, was diving when the 10lbs 4oz lobster approached him near Weymouth jetty, in Dorset, yards from where children were swimming.

He was forced to wrestle the creature, estimated to be 50 years old, into a string bag after it scuttled towards him with snapping claws on Saturday.

Mr Hovard said: "I was diving when I spotted an old boiler which I believe may have been used in the Nothe Fort in the olden days and then was thrown into the sea when it was no longer needed.

"I was swimming around it when the lobster came at me, its claws snapping.

"I could hardly get my hand across the back of its shell. You'd need a saddle to ride it. I managed to get it with a pincer movement."

He added: "The commotion stirred up a silt cloud which momentarily stunned him and this was when I managed to grab him."

Mr Hovard, who lives in Wyke Regis, Dorset, has been diving for 34 years and said he has never seen a lobster anywhere near this size.

He took the lobster, nicknamed Lemmy after the singer in rock band Motorhead, to the Sea Life Park in Weymouth where it has gone on display.

The Northe Fort is a restored Victorian fort now used as museum.