Use seawater or vinegar to treat jellyfish stings, not urine

But according to the British Red Cross, the widespread belief that urine can lessen the pain of venom injected by the marine creatures is misplaced.

It says the substance has the wrong chemical make-up for the job, and that seawater or vinegar is more effective.

The advice comes after conservationists claimed that the number of jellyfish off the coast of Britain is on the rise.

Last month swarms of moon jellyfish led to the closure of a nuclear power plant in Scotland by blocking its cooling water filters.

As families head to the seaside this weekend at the start of the school summer holidays, Joe Mulligan, head of first aid at the British Red Cross, said: “A sting from a jellyfish can be extremely painful, but trying to treat it with urine isn’t going to make your day any better.

“Urine just doesn’t have the right chemical make-up to solve the problem.”

He went on: “If people have been stung, they need to get out of the water to avoid getting stung again. Once out, slowly pouring seawater over the sting will help ease the pain.

“Doing the same thing with vinegar can be even more effective as the acid helps neutralise the jellyfish sting. But, unless you’re near a chip shop, seawater will probably be easier to find.”

Although described by some as an “old wives’ tale”, the belief that urinating on a jellyfish sting will lessen its pain became far more widespread after it featured in an episode of the American sitcom Friends.