More than 27,000 people have joined in a cycle trip from the capital to the south coast in this year's London to Brighton Bike Ride.
Participants began the 54-mile (87km) journey in staggered starts from 0600 BST, with the aim of reaching the seafront in an average of six hours.
The annual ride, which passes through Surrey, is to raise money for the British Heart Foundation (BHF).
It is thought to be Europe's largest charity cycling event.
BHF spokeswoman Gemma Cloke said: "It was quite chilly this morning, but everyone set off without any problems.
"So far, we've been lucky with the weather. There's a lot of cloud, but it's ideal conditions really, not too hot which can cause problems with sunburn."
She said participants were from "across the spectrum" including more seasoned cyclists to those taking part with friends and family in memory of people they had lost.
A husband and wife were taking part on a tandem, she said.
And others were in fancy dress, with costumes including lots of hearts, and a Santa Claus.
She said: "People are always pleased knowing the money is going to a good cause.
"There is so much support along the route, with local residents watching the ride.
"One of the highlights for participants is coming along the seafront while people are clapping, which can really help when they've been in the saddle for a long time."
The gruelling journey started at Clapham Common in south London. Some of the cyclists were as young as 14 and some were in their 70s.
Money raised will be used by the charity to continue research into heart disease, and development of care and support services. Last year, the bike ride raised £4.1m.
Among those taking part was BBC Breakfast's resident GP Dr Rosemary Leonard and several of her colleagues.