An annual open-air Christmas Day swimming race was cancelled after the cold weather left the water frozen.
Members of the Serpentine Swimming Club arrived at London's Hyde Park to find the 100-yard race postponed because of ice.
But that failed to stop around 40 people jumping into an area of the lake where the ice had been broken up.
Some wore Santa hats while others drank hot tea as they tried to cope with the bitterly cold temperatures in the water.
Club secretary Brian Thomas said: "We just went for a quick dip and a wade in the ice. It was chilly but invigorating. I got in, splashed around a bit and got out again. We're not stupid so we don't stay in for ages."
The race was first held in 1864 and the Peter Pan Cup has been awarded since 1904 when it was introduced by novelist Sir James Barrie.
Mr Thomas said it was the first time the Serpentine had been iced over on Christmas Day morning since 1981. "It was disappointing as it's obviously a big event. We have races every Saturday morning but this is the one everybody wants to win," Mr Thomas said.
Members of England's oldest swimming club braved the chilly sea to take part in their annual Christmas Day dip in the English Channel, where the temperature was a refreshing 3.3C.
More than 30 members of the 300-strong Brighton Swimming Club - celebrating its 150th anniversary this year - made up most of the contingent, with hundreds of well wrapped-up spectators looking on.
Club chairman John Ottaway, who has been doing Christmas Day sea swims for 25 years, said: "It's the coldest I have experienced in December and about 2.5 degrees colder than usual. We have had February sea temperatures in December. They call it global warming, I think, but I don't know about that."