A marine heatwave has seen octopus numbers explode in British waters, with experts warning of an ‘extreme’ temperature spike 5C above the norm. The molluscs are gathering in huge numbers around Cornwall and Devon, where fishermen are raking in record profits from selling their meat.It comes as Britain braces for its longest heatwave in 50 years with 35C temperatures and scorching weather set to continue for 14 days. Experts predict a 'Super El Niño' weather event later this year could push global temperatures higher – but its impact is unlikely to be felt in the UK until 2027.Some English fishermen are making more than £20,000 a week after hauling in catches weighing up to 20 tons. But it's not all good news for the UK fishing industry, with chip shop staples cod and haddock moving further north towards cooler waters. Octopuses have also been gorging on lobsters and crabs, taking a toll on some of the South West's most valuable catches. Cornwall has issued an emergency bylaw banning larger ships from using pots to fish for octopus because they also trap lobsters and crabs and make them easy prey.The spike in octopus numbers began in 2025 before surging further this year as even warmer waters drifted in. It means the population is now at its highest level in 75 years.British trawlers caught around 3,500 tons last year, but that quantity had already been smashed by May this year. Fishermen in Brixham landed about 200 tons in a week recently, according to a seafood wholesaler. Octopus meat is considered something of a niche choice among British diners, meaning supply is far eclipsing demand and consumer prices have plummeted. Devon fisherman Malcolm Church with an octopus he found in a lobster pot earlier this year