Jane Tomlinson will undergo two sessions during her three-week ride

But first Jane Tomlinson, of Rothwell, Leeds, intends to complete a 51-mile leg from Braemar to Perth.

A Yorkshire businessman has offered to fly Mrs Tomlinson to and from her regular treatment session to allow her to be back in Scotland to resume her tandem bike ride on Friday.

Her husband Mike Tomlinson said: "The days up to and including Sunday will decide whether Jane will manage this challenge.

"It doesn't promise to be anything other than very difficult."

There's no doubt the physical demands are taking their strain Mike Tomlinson

Mrs Tomlinson, 38, is in the sixth day and steepest part of her 1,060-mile challenge with brother Luke.

The previous days have left the mother-of-three feeling unwell and Mr Tomlinson added: "It was a bit of a monster and Jane was quite distressed.

"There's no doubt the physical demands are taking their strain."

Last year Mrs Tomlinson raised �118,000 for charity taking part in the London Marathon, the Triathlon and the Great North Run.

She has already raised �29,000 in 2003 which will be split between Cancer Research UK, Sport Aided Research for Kids, Leeds Hospital Trust paediatric services and local care centre Hannah House.

Her challenges have won her 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.