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
West Country neighbours meet for first time this season at Kingsholm in Premiership
The funeral of a mother and newborn baby found dead after going missing from a maternity hospital took place today.
A coroner has called for safety improvements at an Austrian ski resort after a Taunton student was killed while not wearing a helmet.