Mrs Tomlinson with Luke, her brother and cycling partner

Jane Tomlinson, from Rothwell, Leeds, will have to undergo chemotherapy during the three-week charity challenge.

The 38-year-old mother-of-three is travelling on a tandem bike with her brother, Luke Goward.

It is expected to be her last big fundraising project.

Starting in Scotland at 0830 GMT on Friday, she plans to cycle 50 miles on her first day, including a climb of 3,435ft.

On 26 March she will have to return to Leeds for chemotherapy, before being taken back to Perth in Scotland to continue the journey.

She is strong and she has trained very hard and prepared very thoroughly Mike Tomlinson, husband

Mrs Tomlinson said: "I'm really looking forward to what I hope will be a big adventure.

"I'm sure it will be very demanding and with luck I hope to get to the finish.

"I can't think of better way of seeing the country.

Mrs Tomlinson has already raised more than �100,000 for Cancer Research UK.

Last year she completed the London Marathon, the Great North Run, and the London Triathlon.

Health risks

She has also won a number of high-profile awards, including The Sunday Times sportswoman of the year and BBC sports personality of the year's Helen Rollason award.

Her husband, Mike, who is at home with the children, said: "The biggest risks are if her haemoglobin levels drop, as she will have to be hospitalised immediately.

"The other risk is that she could get a fracture.

"Because she has cancer throughout her bones, they are more susceptible and the pounding they will take during this bike ride puts her more at risk.

"However, she is strong and she has trained very hard and prepared very thoroughly."