Gary Barlow, Chris Evans, James May and Brian Cox have set off from Lands End in a pink Rolls Royce raising money for Breast Cancer Care.
The challenge will see them driving from Land's End to John O'Groats in a bespoke pink Rolls Royce Ghost.
They want to try and raise £1 million in 24 hours.
The four celebrities will stop off in Bristol as part of their trip.
More top news
An inquest heard that Emma Welch, from Chlicompton, suffered internal bleeding after a spinal operation.
Elderly and vulnerable people in Dorset have been conned out of more than a million pounds in two years by 'phone fraud' gangs.
Mike Brandon has terminal cancer but his wife Kate is desperately trying to raise the money to access potentially life saving treatment.