Double Olympic winner Dame Kelly Holmes has credited the music of Prince for keeping her relaxed as she took on her first marathon alongside thousands of others in a record-breaking year for the race.
Organisers said more than 39,000 people were due at the start line for the 36th London marathon, which will see its one millionth competitor cross the finish line on Sunday.
British astronaut Tim Peake may have been miles away in space but he was just behind Dame Kelly in terms of time, claiming a new Guinness World Records title for the fastest marathon in orbit.
The spaceman, who ran the marathon while strapped to a treadmill 400km above earth on board the International Space Station, completed it in three hours and 35 minutes, just minutes behind Dame Kelly's finish time of three hours and 11 minutes.
Major Peake had sent a good luck video message to racegoers as they set off on a chilly but bright day, with supporters lining the capital's streets.
Dame Kelly was one of a host of big names signed up for this year's event including Top Gear host Chris Evans and Game of Thrones actress Natalie Dormer.
Speaking after the race she said she felt happy but sore.
She told the Press Association: "I'm really proud of myself, I'm in a bit of pain now obviously. My legs are aching beyond belief. But it is an amazing feeling to think I've done it."
Asked would she do it again she said: "At this moment no."
The sportswoman, who had her nails painted different colours honouring experienced runner Eddie Izzard, the Queen and Prince, said the musician, who died last week, helped keep her calm.
She said: "At nine miles I had Purple Rain on, I was loving it. At nine miles I needed to calm. I felt so good and the crowd were brilliant. That came on and I had a little bit of a smile because I had my nails painted for him as well."
She added: "He kept me in control. When he came on I was like 'smile, relax' and that's what I did."
In the elite men's race Kenyan Eliud Kipchoge successfully defended his 2015 title, completing the course in a record time, while fellow Kenyan Jemima Sumgong won the elite women's race.
Maj Peake was one of scores of entrants attempting to break Guinness World Records this year as fun runners took part in an event that attracts elite athletes and fundraisers alike.
There are 70 years between the oldest and youngest runners in this year's race.
Race veteran Iva Barr, 88, from Bedford is running her 20th London Marathon, while Rebecca Manners from Manningtree in Essex is celebrating her 18th birthday by running the route alongside her parents.
The marathon's chosen charity for next year was announced on Sunday as competitors set off.
Heads Together, which will take over from the NSPCC, is made up of a team of mental health charities which have been brought together by The Royal Foundation of the Duke and Duchess of Cambridge and Prince Harry, who is patron of the London Marathon Charitable Trust.
Runners set off from Blackheath and Greenwich Park, running a route lined with supporters, and finish on The Mall.