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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A runner from Bristol is about to embark upon a marathon challenge around the UK, running 26 miles every day for more than a year.
People have been paying tribute to the victim of a suspected hit and run in Bristol, who has been named locally as Dan Hickey.
Church attendance may be falling across the country, but church tourism is on the increase.