While most Londoners were in bed nursing hangovers, Hampstead’s hardy womenfolk were plunging into icy waters.

The New Year’s Day swim is a Hampstead Heath tradition dating back to the 1980s.

Last year was the coldest in memory with near-frozen waters. But this year, the mercury reached a balmy six degrees – luring unsuspecting novices into thinking the waters would be warm.

“It was like a thousand icicles,” said New Barnet resident Marion Firth. “I’ve been here on a hot summer’s day but I hadn’t experienced the New Year’s Day swim.”

“It literally burns,” added lifeguard and opera singer Camilla Ball. “Pretty soon you can’t feel your hands and feet which is why people wear gloves and boots. Personally, I don’t dive in below seven degrees – it’s too much of a shock for the body.”

After initial gasps and prayers, hoots and squeals, beaming swimmers admitted the shock was worth it.

“It’s so invigorating. It makes you feel fantastic afterwards,” said Mrs Firth.

“It’s a great way to start the year,” added Miss Ball.

Crowds of Heath walkers watched from afar – mystified by the valiant ladies’ antics. But for the growing band of pond devotees, the allure of the outdoor plunge is clear.

“A lot of people who come here say it’s changed their life,” said Tulay Denirtas. “The peace and the space is totally unique and it’s liberating.”

“There’s so many strong women here, full of bravery and willingness to take on challenges,” said Penny Green from Clerkenwell.

The ponds have a reputation for attracting the eminent and the wacky from Hampstead and Highgate.

While some swimmers gingerly lowered themselves in and made an immediate dash for the steps, others swam several laps or lay back and contemplated the scenery and the wildlife.

One lady wore kitchen marigolds to swim and another wore a bobble hat, while others followed certain rituals after the event.

Swimming buddies Diane Thomas and Clare Bennett-Carter from Queen’s Park and Willesden revealed that post-swim bliss started with getting changed standing in a bucket of hot water and drinking tea before going home to slow-cooked porridge with maple syrup.

More than 50 ladies celebrated their exertions with mulled wine and festive treats in the outdoor gazebo party hosted by the Kenwood Ladies’ Pond Association (KLPA). “Every year it is the same and yet different,” said KLPA committee member Margaret Dickinson.

“This year we’re very pleased to have had so many first-time swimmers.”