There aren't many people who can say they've beaten Sherlock Holmes. Fewer still who've done it with a smile on their face. But that'll be Andy Jackson's claim if he crosses the Virgin London Marathon finish line on Sunday in less than four hours one minute.

Jackson will be wearing his round, yellow and beaming Mr Happy suit as he hopes to claim the Guinness world record set by Ian Young (disguised as Holmes) last year as the fastest marathon run while dressed as a book character.

"Ideally I'd like to go under four hours," said Jackson. "But I can confirm that Watson won't be with me."

Mr Happy's quest for the record books is even more impressive, however, for Jackson is only two-thirds through a running journey from John O'Groats to Land's End to raise £200,000 for Children with Leukaemia, a disease the 26-year-old Jackson suffered from himself eight years ago.

"I feel remarkably good, actually," said Jackson. "But this race will be the longest stage of the whole 10-week challenge. We've done 700 and something miles so far."

It's not miles on Steve Chalke's mind, but money. The 55-year-old south Londoner is aiming to break his own world record for the most money raised at a single sporting event - the more-than-princely sum of £2 million being his target.

Chalke took the record from Olympic legend Steve Redgrave a few years ago, driven by his desire to raise funds for Oasis, the organisation he set up in 1985 to organise life-transforming initiatives for young people around the world.

The 55-year-old, a United Nations special advisor in human trafficking, is also aiming to finish in less than four hours, which will make him, he claims, "the fastest money raising sportsman of all time".

"Even if you add up all the prize money made by Tiger Woods, Roger Federer, and other top sportsmen, it wouldn't be as much money as I'm going to raise in a short time," he said.

John Coleman's motivation is somewhat different. The Star Man, as he's become known is doing it all for the love of his favourite charity, Starlight, who raise money to help terminally ill children. The 65-year-old Watford man has run 12 London Marathons, 23 in total, but this time he hopes to come out with a record as the fastest star to complete the distance.

"I need to beat 6 hours 36," said Coleman. "That's not very fast, but in a costume it's going to be very hard. But I will do it because I dedicate myself to the charity. I love what they do."

Coleman's costume is a rather unwieldy five-pointed contraption that covers his whole body. Eleanor Franks had a different strategy - she merely picked a costume she'd always wanted to wear: a wedding dress.

"I had the idea ages ago," she said. "I just thought I'd always wanted one so why not run in one?

"But that was before my fiancé proposed, and now I am getting married on 23 July. So since I started planning it, the idea's become more topical. There's the Royal wedding too. I just think this is the year.

Franks needs to finish in under 3:50 to claim the record, but with eight marathons behind her, she's more than capable. In 2008 she finished in 3:59:49 attempting to become the fastest female superhero. She's also raising money for Yorkshire Cancer Care after two of her friends were treated for breast cancer.

There are 156 Guinness attemptees this year, including a 20-person marching band and 50 in a centipede. Not all of them will break records, but they'd all do well to heed Mr Happy's parting advice: "Just grit your teeth and bear it," said Jackson. "It's amazing what you can get through if you need to."