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
The Moon balloon created especially for the Bristol Balloon Fiesta, is going to return to the city in 2017.
Long-distance swimmer Ben Hooper says being stung by a Portuguese man of war was 'worse than any of the stings he'd had so far'.
There's rain on the way but it'll stay mild, with a dry outlook for Sunday. Bob has the forecast...