Ms Wilkins made the decision to run the 26.2-mile race after meeting Kevin Green, an entrepreneur who donated money to Children's Hospice South West, as part of Channel 4 television programme The Secret Millionaire.

Mr Green was inspired by Ms Wilkins during filming and donated money to send the family to Florida so Shannon and her sisters would have the chance to swim with dolphins.

Ms Wilkins said: "This time last year I couldn't run one mile so this is a big challenge for me. I met Kevin when he was filming The Secret Millionaire programme. I thought he was making a documentary so it was quite a surprise to find out he was a millionaire.

"He decided to give money to Little Bridge House, the hospice, and I suppose he was inspired by Shannon and me and sent us to Florida.

"We went in September and it was an amazing experience. Shannon is physically disabled and life-limited.

"She can't talk or walk and can't really respond but to see her face light up... I just can't describe it."

After the show Mr Green said he was planning to run the London Marathon and asked Ms Wilkins if she would take part in his team, which also includes his friends, BBC presenter Martin Roberts and Greg Ellis.

"I try to keep fit and go to aerobics but I'd never run before," Ms Wilkins said. "I had a heart operation a year-and-a-half ago so I couldn't even run one mile. I'm raising money for the AMBER foundation, which helps rehabilitate wayward kids. Training and fundraising is going well.

"Running is great. I look after Shannon and my other daughters 24/7 so it is really a release and a chance to go out and get away from everything. It's just me, my music and the road."

After completing the Taunton Half Marathon last weekend with a time of 2hrs 5min, Ms Wilkins said she is hoping to complete the London Marathon in four hours.

"I think it's a tall order but we'll do what we can," she said. "I'm hoping the crowds and the atmosphere will keep me going."

To sponsor Ms Wilkins visit www.justgiving.com/2010adele.