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.
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Earlier this evening we had more clear spells appearing and they prompted a fall in temperatures.
Cold particularly in Dorset and Somerset. Close to freezing.
Colin Durston was due an operation for a permanent replacement before Christmas but the winter crisis has left him unsure about the future.