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
Police have launched a murder investigation following the suspicious death of a man in his 20s in Plymouth.
It's looking like it'll be a dry night, with sunny spells tomorrow. Here's Helen with your forecast.
Tonight will be dry with clear spells for most, although there may be some isolated fog patches as we head towards the early hours.