Singer Boy George joins in the celebrations on his own float
Rubber suits, drag costumes and knee-high boots were the order of the day as central London was awash with colour during the annual Pride celebrations.
The parade, celebrating gay, lesbian, bisexual and transgender culture, brought the West End to a standstill.
Up to 500,000 marchers gathered in Trafalgar Square for a party with live music and dancing.
Protests by right-wing and church groups against the promotion of homosexuality failed to damped spirits.
Prime Minister Gordon Brown had met organisers at Downing Street ahead of the march.
Among the equalities campaigners who attended the garden party at Number 10 was festival patron and comic Rhona Cameron, who led the parade.
It's not just enough to be out and proud today - we have to be out and proud every day
Richard Barnes, Deputy Mayor of London
Mr Brown's wife, Sarah, wore colourful necklaces over black clothes and carried a pink, red and white version of the union jack as she joined the head of the march.
Thousands of people lined the route of the parade, some dressed as flamboyantly as the participants.
The marchers as they made their way along Oxford Street, followed by drag queens in huge blonde wigs and union jack outfits.
One group in Regent Street wore rubber suits and masks decorated with ropes.
A drag queen, wearing a dress made from plastic sheeting and used drink cans, also caused a stir - and lots of noise - when she walked past.
Perhaps the noisiest participants were the representatives from the London emergency services who marched as sirens sounded from a fire engine and an ambulance.
There were big crowds at Piccadilly Circus, where a man dressed in knee-high boots, pants and a Native American feather head-dress danced beneath the statue of Eros.
There was a carnival atmosphere as the parade marched through London
A small, peaceful group of National Front protesters held banners saying "stop the promotion of homosexuality" from behind a barrier at the bottom or Regent Street.
Two men were cheered by crowds as they kissed in front of the protesters, who did not react.
Another group of around 30 protesters preached through a loudspeaker and held signs saying homosexuality was against God's wishes.
Thousands of people gathered in Trafalgar Square, where former M People vocalist Heather Small was cheered as she took to the stage to sing Proud.
Mayor of London Boris Johnson was unable to attend, but sent a video message which said: "I want to say how proud I am to be supporting this great, great occasion."
He said Pride sent out a message to the world that London was open, generous and welcoming.
However, many in the crowd booed when he appeared on the screen.
Deputy mayor, Richard Barnes, took to the stage and told the crowd: "It's not just enough to be out and proud today. We have to be out and proud every day."
The Prime Minister had described the creation of civil partnerships as one of a set of "massive strides towards equality" for the gay community made under Labour - "often in the face of fierce opposition".
"This government is committed to standing at your shoulders in the fight for equality and we are guided by one very simple principle when it comes to LGBT rights: you can't legislate love," he said.
However, Pride founder Peter Tatchell has described civil partnerships for same-sex couples as "a form of sexual apartheid".
He said on Friday he was planning to press Mrs Brown to speak to her husband about giving gay people the right to marry in the same way as heterosexual couples.
During the march, Mr Tatchell carried a sign saying: "Gordon and Sarah can marry, gays can't. End the ban on gay marriage."
Last week, a political row was triggered when Culture Secretary Ben Bradshaw, who is openly gay, told a public debate there remained a "deep strain of homophobia" running through the Conservative Party.
It provoked an angry reaction from Alan Duncan, one of two gay members of the shadow cabinet, who accused Labour of "poisonous mudslinging" in a bid to stir up hatred and reopen old divisions.
"It is deeply unworthy and unjustified," he said.
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