For most rational people it is a time for slobbing out of the sofa, chain-watching Harry Potter movies and mainlining Quality Street. For an increasing number of festive fun-seekers, however, taking part in an organised activity during Twixtmas – which kicks off on Christmas Day and finishing on New Year’s Day – is now as much a part of the calendar as the Queen’s speech or getting irate with your relatives.

On Christmas Day thousands of swimmers, many of them donning their bathers for charity, gathered for icy dips in places from Tenby to Torquay or met up for the annual yuletide park run. Large-scale ball games of Uppies and Downies, a sporting endeavour with varying rules, kicked off in a towns including Workington in Cumbria and Kirkwall in Orkney, where it is called the Ba’ game. And should you be lucky enough to find yourself in the picturesque Cotswolds this Boxing Day, it would be near criminal not to take part in the famous Bibury duck race.

Ball’s up or doon? Residents of Kirkwall, Orkney, enjoy the rough and tumble of the Ba’ game. Photograph: David Gowans/Alamy Stock Photo

So why are so many people taking part in slightly oddball pastimes over the Christmas period? Ella Foote from the Outdoor Swimming Society says the number of people ready and willing to take a icy dip before the end of the year is growing year on year.

“It’s definitely become a huge thing, and attracts a lot of people that only do it at this time of year,” says Foote, who has been raising money for the mental health charity Mind by taking a cold-water dip every day this month. “For swimmers particularly it’s become a really social thing, Christmas dinner tastes a lot better if you’ve swam in cold water in the morning.”

The members-only Christmas Day swim in the Serpentine, Hyde Park, London, now has to be limited to 70 participants for safety reasons, says Robin Hunter, the president of the Serpentine Swimming Club. The swim has taken place since 1864, and carried on throughout all the war years. “Whether trying to raise sponsorship or visibility for their activity, we do it because a bunch of people started 150 odd years ago and we’re keeping up the tradition,” he says.

Swimmers take part in the Christmas Day swim in the Serpentine in London. Photograph: Andy Rain/EPA

A festive run has also become quite normal. Five years ago there were 101 Christmas Day park runs, but this year there were 400. Three-mile park runs are weekly event across the UK. Andy Evans, the event director of the Tring park run in Hertfordshire, says about 100 runners came to the first Christmas run four years ago, but that this year he is expecting 250.

“Lots of our runners come week after week, so it feels natural to see them on Christmas day,” he says. “Particularly for people who might be on their own at Christmas, and who won’t get a family visit it is an event to go where you will see your wider social family.”

Bibury has not one but two duck races on Boxing Day. Photograph: Phil Wills/Alamy Stock Photo

Boxing Day events include two duck races in Bibury, where thousands of plastic ducks race under the village’s bridges to raise money for charities and the local cricket club. It’s all very jolly, says Terry Day, the founder of the event and the cricket club’s groundsman. “It’s very popular and the club put on mince pies and mulled wine. We have visitors from around the world, but it’s great to see all the villagers come together.”

It’s a bit of fun, but a big event in the village’s calendar, says Virginia Ryselyte, the reception manager at the Swan hotel: “It’s a lovely family day, but oh my goodness it gets competitive.”

Other events are a bit more rough and tumble. The Ba’ game in Kirkwall, Orkney, involves the whole town split into two teams –the Uppies and the Doonies. The Uppies have to get the ball to a marked wall high up in the town, while the Doonies try to get it to the harbour. Teams can be up to 100 strong and the game, which dates back to at least the late 19th century, draws about 1,000 onlookers, according to Charles Tait, a local photographer who has an exhibition chronicling the history of the event on at Kirkwall’s Old Library.

A Ba’ game bookends the festive period for Orcadians, with the final match held on New Year’s Day. If it sounds like a lot of effort from the comfort of your sofa, it is – but it’s worth it, says Tait. “It’s taken very seriously. It’s far more important than Christmas dinner.”