Jane Tomlinson is determined to raise £1 million

The 40-year-old, from Rothwell, near Leeds, is taking part in the Half-Ironman UK Triathlon on Sunday.

It is the second time she has been involved in the event in Dorset which includes a 1.2-mile swim, a 56-mile bike ride and 13.1-mile run.

Mrs Tomlinson finished in six hours and 28 minutes last year.

It was the first time anyone with terminal cancer had attempted the event, but Mrs Tomlinson's breast cancer is now in a more advanced stage and chemotherapy has damaged her heart.

The fact that Jane is a British person achieving things no one in the world has, leaves us with an enormous sense of pride Mike Tomlinson

Earlier this month she completed the London Triathlon for the third time and in July she took part in the Salford Triathlon alongside her daughters Suzanne, 19, and Rebecca, 16.

This is despite vowing she would not do any more challenges after finishing her epic 36-day bike ride from Rome to Leeds in June.

Her husband Mike, 43, said the support they had received from thousands of people had encouraged her to carry on.

He said: "We receive thousands of letters saying that people seeing Jane competing gives them hope, and that alone is enough for us. The money is a bonus.

"The fact that Jane is a British person achieving things no one in the world has, leaves us with an enormous sense of pride."

Mrs Tomlinson has already raised £850,000 for charity.

The triathlon is at Sherborne Castle.