* Click here to watch latest YEP news and sport video reports.

But as Holly, 27, and Sam, 24, have the advantage of youth on their side, they have decided to give their father a sporting chance - the pair will be competing as part of a 32-strong human caterpillar.

* Click here for latest YEP news and sport picture slideshows.

"It's going to be exciting. Dad is certain he is going to beat us but I feel 64 young legs will surely give us the edge," Holly said.

"It really will be a challenge. Already in training we are experiencing minor problems and are particularly worried about the loo stops on the day, especially with 32 of us tied together."

The siblings hope to complete the full 26.2 miles tied to each other and aim to set a world record for the highest number of runners to cross the finish line together.

The cash they raise will benefit 12 children's charities, including Kids Company which has enlisted a group of youngsters to design their multi-coloured costume.

Holly, who works for Virgin, added: "It will be worth all the laughter at our expense if we raise lots of money to support 12 incredible UK charities. Oh, and the fact that we get to show our dad how it's done."

But Sir Richard will be leaving nothing to chance and has already been fitting training around his punishing work schedule.

"My kids have decided to challenge me so they've created this giant caterpillar. They've said dad's 60 years old and the caterpillar can beat me," he said.

However the business tycoon is determined to cross the line ahead of them.

"I've been travelling non-stop and so far I've done training in about 15 different countries - having to get up and get over the jet lag and go running has been quite difficult.

"I did a 12-mile run about two days ago and seemed to survive so hopefully I'll get around. All I want is to beat the caterpillar - that's all that matters," he added.

The Virgin boss will be running alongside TV presenter Jenni Falconer, singers Natalie Imbruglia and Michelle Heaton, Hollyoaks' Ricky Whittle and Kenyan marathon champion Tegla Loroupe.

The group will be fundraising for Virgin Unite - the non-profit foundation of the Virgin Group which supports vulnerable young people in Britain.

For every five pounds donors make to the Virgin Money Giving page, Sir Richard is offering a chance in a prize draw for a trip for two to his private Necker Island, in the British Virgin Islands.

Branson's Virgin Money signed a £17m, five-year deal to become the official sponsor of the London Marathon in May 2008.