Vic Reeves and wife Nancy Sorrell will also team up for an I'm a Celebrity... Get Me Out of Here! special of the quiz show hosted by Chris Tarrant.
The comedian will be raising money for animal rescue charity the Born Free Foundation, while Sorrell will be playing for medical research charity Tommy's.
Former winner Joe Pasquale will also answer questions for the drug and alcohol rehab centre Focus 12, with Tufnell attempting to raise funds for the Teenage Cancer Trust.
Meanwhile, Gest will be playing for Liverpool's homeless charity The Whitechapel Centre, and will team up with Jennie Bond, who will raise money for the Devon Air Ambulance service.
The special live episode will air on Friday, November 9 at 9pm on ITV1.
The 12th series of I'm a Celebrity will premiere two days later on Sunday, November 11 with a 95-minute special.
Celebrities rumoured to be taking part this year include darts veteran Eric Bristow, soap star Ricky Groves, Corrie's Helen Flanagan, Birds of a Feather actress Linda Robson and fashion advisers Trinny and Susannah.