It’s time to dig your favourite festive knit out the back of the wardrobe.

ITV’s Text Santa appeal is urging the nation to don their Yuletide woollies on December 18 for their annual charity Christmas Jumper Day.

Phillip Schofield for Text Santa
Phillip Schofield demonstrates a fetching reindeer design (ITV)

Sweater-wearers can then tune in for a three-hour TV spectacular that last year saw George Clooney join the cast of Downton Abbey, Phillip Schofield abseil the Shard and special sketches from ITV shows like Birds Of A Feather and Coronation Street.

A special celebrity edition of Ninja Warrior UK has already been filmed, featuring Mark Wright, boxer Carl Froch, ex-Pussycat Doll Kimberley Wyatt, and skating legends Jayne Torvill and Christopher Dean among others.

Text Santa is now in its fifth year and has so far raised £21 million for UK charities. This year, it will be raising cash for three charities: Macmillan Cancer Support, Make-A-Wish UK and Save the Children.

Text Santa shot of George Clooney and Hugh Bonneville
Last year’s Text Santa appeal featured George Clooney in Downton Abbey (Nick Briggs/ITV/PA)

Festive fundraising events will kick off on  December 1 this year and London’s largest Santa run and country-wide Christmas pub quizzes are planned to encourage the UK to dig deep.

Peter Fincham, ITV’s director of television, said: ”Text Santa is ITV’s annual flagship fundraiser and this year we are asking everyone to join us in showing their support, both in the lead up and on the big day itself, by taking part in fundraising, and wearing a Christmas jumper on the 18th.

“With our partners this year in Macmillan Cancer Support, Make-A-Wish, and Save The Children, we are looking forward to making December 18th a big one for ITV – encouraging our viewers to get involved with Christmas Jumper Day, and that evening, broadcasting live with Text Santa for our biggest and best entertainment spectacular yet.”

Phillip Schofield is presenting Text Santa
We all know what mistletoe means, Phil… (ITV)

Appeal partners for 2015 include Papa John’s, Vodafone, Twentieth Century Fox and department store Liberty.

Through last year’s appeal, generous viewers helped to provide 45,000 hours of specialist care to young people fighting cancer, support more than 3,600 people suffering from dementia, and provide 51,650 hours of care to children and their families.

Visit ITV.com/textsanta for more information on how to get involved and order a fundraising pack.