First time nerves for famous five

"No way." "Not in a million years." "You must be joking."

To many of London 's celebrity runners, the thought of running a whole marathon seemed, at one time, the height of complete madness. But come Sunday morning they will be out there anyway, overcoming their first-time nerves to pound the capital's streets in pursuit of personal pride, specific goals and as much publicity as they can muster in 26.2 miles – all in the aid of a good cause or three.

"I had a real dislike of running," said EastEnders actress Kara Tointon, who's aiming to raise £6,000 for Cancer Research UK.

"My friend persuaded me to start doing it. I put myself down for the Great North Run and enjoyed that, so here I am," said the 23-year-old who plays Dawn Swann in the BBC soap.

"But I'm a real amateur runner," she laughed. "Finishing in eight hours would be good, as long as I finish before that guy in the heavy diving suit. I just don't want to embarrass myself and do a Jade Goody."

Tointon decided to enter her first Flora London Marathon after Lynn Fox, a close family friend, died of breast cancer while training to run it herself.

"I was at her funeral when I decided to do it in her memory," said Tointon, who will run with six of Lynn's friends. "Lynn had been training in the hope of running, to celebrate ten years since being given the all-clear following her first bout of breast cancer.

"None of us have ever run one before so I'm sure it will be very emotional at the finish. But we've all got strong hearts and we're all looking forward to taking part."

Just as it is for most of the 36,000 hardy souls who will be sweating through London's streets on Sunday, 'taking part' will be the order of the day for the celebrities – even for those with considerable sporting pedigree of their own.

Matt Dawson was a Rugby World Cup winner with the England team just three and half years ago but "there was no way I was ever going to do a marathon until I saw it," he said. "Never in a million years. But it just whisked me away when I felt the atmosphere and excitement. It was inspiring."

Dawson went to watch in support of his girlfriend, Joanne, but this year he'll be dragging his own body from Blackheath to the Mall as one of Flora's First Timers. Together with Olympic gold-medal-winning hurdler Sally Gunnell, he's been supporting a swathe of 10,000 people who are also making their marathon debuts on Sunday.

"The great thing about Flora, and working with Sally, is that we're representing all these other runners who are in the same boat as us," said Dawson, who's become a familiar face on BBC TV's 'A Question of Sport' since the end of his rugby career. Like Gunnell, Dawson is raising money for WellChild, official charity of the 2007 London Marathon, as well as Heart UK , and both will be wearing red laces to highlight Flora's family fitness campaign.

"I've spent all my life competing and keeping fit," he said, explaining his conversion to running. "I needed to get into something that I could do for the rest of my life. I tried running initially just to stay healthy but since I started training for this I've really got into it."

It's a familiar tale among London celebrities. Yachtswoman Dee Caffari is used to lonely voyages of discovery – after all, she was the first woman to sail single-handedly around the world 'the wrong way' – but even she admitted to trepidation at the prospect of covering 26 miles without a rudder.

"I am definitely a sailor not a runner," she laughed. "I learned that pretty quickly. "But running is an addiction and I have got into it. Now I even have a target time. I want to get close to four and a half hours.

"But I am worried about being too excited at the start and going off too fast. The last few miles are going to be like sailing through a storm. Shame I can't have a back-up plan and put up a mainsail to get me through."

Even for an ex-athlete, the thought of facing your first marathon is daunting. "It's worse than the Olympic final," joked Gunnell. "I'm very nervous. It's going to be quite a challenge. Going once round a track over 10 hurdles is very different to running 26 miles."

Gunnell is leading the Flora-led Families Get Active campaign to persuade families that staying fit doesn't have to mean running a marathon. Unfortunately, she has to do one herself to promote the campaign.

"I had to go back to having a training plan and everything," said the former athlete who's been running over the South Downs to get in shape. "I really don't want to slow up and get the shakes. I still find the thought of it quite daunting.

"But I've worked on it for years as a TV interviewer and deep down I thought I ought to go over to the other side and feel what all these people feel. So when Flora approached me I thought, 'Yep, this is it'. And now it's kind of taken over my life."

Disabled from an early age, TV presenter and wheelchair basketball player Ade Adepitan has faced more than a few challenges in his life. But he was keen to stress his credentials as a marathon novice.

"I'm more used to pushing about on a basketball court," said the Paralympic Games bronze medal winner. "Ninety feet is my record. For the first 90 feet on Sunday I will be the pacemaker."

Adepitan is actually entered in the elite wheelchair race, although he's really racing to raise money for the Brain and Spine Foundation and Wheelpower.

"I would like to do it in under two and half hours," said Adepitan, who like many an elite marathon runner has been training in south-west London's Richmond Park for his Sunday morning baptism. "Something like that would be great. It might be slightly optimistic, but we'll see."

Not all the celebrities are first timers, of course. Model Nell McAndrew is such an accomplished runner – she completed the London course in 3:10:52 two years ago – that she practically qualifies for the championship races.

But 2007 will be different for her too. This year McAndrew is running with her 54-year-old mother, Nancy, to raise money for Cancer Research UK. "I just want to be there when she goes a bit flat," said McAndrew. "My Dad had cancer and he's now in remission, so we are doing it for him.

"She just wants to finish before the sweeper system comes by. It will be a long old day for me. But I'll get a good sun tan, which will be nice, and it'll give me more time to chat with people and enjoy the atmosphere."

Indeed, it could be "a long old day" for many of London's celebrities by the time they reach the Mall sometime on Sunday afternoon. By then, though, the first-time nerves and trepidation will be gone. And all that'll be left – besides the pain – is pride.