British seas have been invaded by huge octopuses taking advantage of local bylaws to devour crabs and lobsters.

Fishermen in Plymouth and Brixton, in Devon have noticed a sudden boom in the numbers and size of common octopus in the last year they say.

There is a long-standing Devon bylaw which means crab pots must have "escape holes" - a conservation requirement to allow younger shellfish to escape."

And now octopuses, reportedly coming from Morocco, have taken advantage of the easy hunting ground and are breaking into crab and lobster pots at an increased rate to eat all the catch inside.

Scallop fisherman Derek Meredith, 57, said he used to pull up 20kg of octopuses a week - but now sees at least half a tonne of the supersized sea creatures.

Derek, from Brixham, and owner of the Golden Promise, said: "It's having a major impact on shellfish."

"A crab fisherman said in the pots he is getting lots of lobster shells - they are eating them in the pots."

"They are here to feed. They are going to follow the food source."

Mike Sharp, 61, owner of four boats based in Brixham, has been fishing since 1980 and owned trawlers since 1988.

He said: "The octopus are eating all the crab. They are eating all the lobsters and all the scallops. "

"There isn't going be any crabs - they are going to eat everything. "

"It is going to be a disaster for the crab industry. I hope I am wrong."

Mark Bolton, 62, a fisherman, relief mate and skipper from Brixham said: "The octopus does have value but they are causing issues for the inshore fisherman and also for the scallopers - the octopus are incredibly strong. I will consider them one of the apex hunters. "

"It is prolific at the minute. A smaller breed of octopus, we used to see maybe one or two boxes for a seven day trip. These things can be up to six feet."

Diver Dom Robinson, 53, has also seen a sudden influx of the animals - something he hasn't seen for 20 years.

He said: "There has been an explosion in large octopus."

"I'm seeing them on loads of dives."

The fishermen believe the boom is down to environmental reasons - rising sea temperatures and reduction in the number of natural predators.

Tom Parker, 37, of JT fishing limited, said: ""The octopus bloom - the last one was in the 50s and it lasted for three years. "

"The water temperature has risen slowly over the years and that could be one of the reasons. They also feed in a lot of shellfish - there is going to have a lot of impact on the shellfish. They eat crab and lobsters - what is going to happen a lot of the crabbers are going to have a big problem when they have to catch them - they won't have any to catch."

It is thought the octopuses are coming from Morocco, as fishermen there are reporting a shortage of the creatures, reports say.

The Devon and Severn Inshore Fisheries and Conservation Authority (IFCA) is responsible for implementing the bylaw and has held an emergency meeting.