Chris Thompson and Jo Pavey were the surprise winners of the men's and women's RunLondon 10km road races.
Radcliffe took 45 minutes to finish after running for fun
Thompson outsprinted Kenya's Luke Kipgosei and fellow Briton Mohamed Farah to win by six seconds in a time of 28 minutes 50 seconds.
Pavey, who finished fifth in the Olympic 5,000m in Athens, won in 32:33.
Marathon world record holder Paula Radcliffe, who was the official race starter, was among the 30,000 running for fun and took 45 minutes to finish.
The New York Marathon winner said: "After New York I wasn't ready for a competitive race, but felt I must support it and accompany some of the fun runners.
"It was really good fun. There was a great atmosphere on the course. There was a really festive spirit because of all the Christmas lights."