It is one of the more unusual insurance policies, even by Simon Burgess's standards.

The underwriting agent has arranged £1m of cover for the National Sea Life Centre in Birmingham in case its newly arrived Japanese Spider Crabs escape from their tanks and attack visitors.

At the age of four the crabs already measure 5ft from end to end, but fully grown they can reach 13ft, with 3ft long claws. They can live up to 100.

The crabs cost the centre £1,500 each, and it cost a further £10,000 to fly them in from Japan.

They have been acclimatizing over here before becoming one of the centre's main draws.

They are to star in the centre's “Claws” display, which will also feature fire shrimps, mantis shrimps and an assortment of lobsters.

Burgess, managing director of Ultraviolet, said he had been contacted on behalf of the centre to arrange cover for the crustaceans because “after Lloyd's I am probably the world leader in bizarre and unusual insurance”.

He said there was a negligible risk the crabs would escape and this was reflected in the cost of the policy. The centre is paying £2,300 for a year's cover.

But he added: “Obviously the risk gets bigger as the crabs get bigger.”

Jon Morton, senior operations manager at the centre, said he doubted it would need to claim on the policy, which covers death or disablement of visitors.

“The crabs will be fine. We've got a toughened glass tank,” he said.

Among the more unusual covers arranged by Burgess is a policy covering the president of the Official Loch Ness Monster Fan Club for £1m, in case he encounters Nessie.

Thew president, Gary Campbell, is covered for post-traumatic stress disorder and death or permanent total disability caused by the monster.