Celebrations at the annual Pride In London event are the "best antidote" to the terror and tragedy of recent weeks, Sadiq Khan has told thousands gathered in the city.

The Mayor of London said this year's event was the biggest ever, as he addressed revellers in Trafalgar Square.

Members of the emergency services who helped in the aftermath of terrorist attacks and the Grenfell Tower fire disaster launched the march.

Staff from the Metropolitan Police, London Ambulance Service and London Fire Brigade were nominated to take part after helping in response to terrorist atrocities and the Grenfell Fire disaster, organisers said.

They joined flag bearers representing countries around the world, including those where it is still illegal to be LGBT+.

Mr Khan told the crowd: "We've had a horrible last few weeks. We've had terror, we've had tragedy. You know what the best antidote to sorrow, the best antidote to sadness, to bereavement, to hatred, is Pride In London."

Mention of the DUP, which the Conservative Government struck a deal with following the general election, drew boos from the crowd.

Mr Khan warned that the arrangement with the Northern Ireland party, which is anti-gay marriage and anti-abortion, would not change the status quo in London.

To huge applause, he said: "You (the Government) may have done a deal with the DUP but there will be no backtracking on LGBT+ rights.

"There will be no backtracking on women's rights."

Many in the crowd booed earlier when a video message from Theresa May was played.

In it, the Prime Minister reiterated the UK's pledge to encourage other countries to ensure equal rights for all, regardless of sexual orientation, and to take a stand against hate crime at home.

She said the UK "will continue to stand up for human rights, directly challenging at the highest political levels governments that criminalise homosexuality or practice violence and discrimination against LGBT+ people".

She added: "And here at home too, we must continue to stand up for true equality and respect for everyone, right across our United Kingdom.

"We must stamp out homophobic bullying in schools, and drive down homophobic and transphobic hate crime."

More than 26,000 people are estimated to have taken part in the parade which began north of Oxford Circus on Regent Street, watched by a crowd expected to number around one million.

London Pride 2017 Show all 14 1 /14 London Pride 2017 London Pride 2017 Revellers in Trafalgar Square in front of the National Portrait gallery take part in London Pride, the Lesbian, Gay, Bisexual, and Transgender (LGBT) parade in London EPA London Pride 2017 A man wearing two hats attends the Pride in London Festival Getty London Pride 2017 Protesters demonstrate during the Pride in London Festival in London. This year's London Pride event marks 50 years since homosexuality was decriminalised in England and Wales under the 1967 Sexual Offences Getty London Pride 2017 The parade passes Nelson's Column as revellers take part in London Pride, the Lesbian, Gay, Bisexual, and Transgender (LGBT) parade in London, EPA London Pride 2017 Members of the Lesbian, Gay, Bisexual and Transgender (LGBT) community take part in the annual Pride Parade in London on July 8 AFP London Pride 2017 Revelers enjoy the Pride London Parade in London. The Parade attracts an estimated crowd of 1 million onlookers, while around 26,500 people are taking part in the annual Parade making this the city's biggest one-day event and one of the world's biggest LGBT+ celebrations. AP London Pride 2017 Revellers take part in London Pride, the Lesbian, Gay, Bisexual, and Transgender (LGBT) parade in London EPA London Pride 2017 A participant sits on a rainbow coloured flag during the Pride in London Parade in central London PA London Pride 2017 Two men sit on a rainbow flag painted on the pavement at Oxford Circus as revellers take part in London Pride, the Lesbian, Gay, Bisexual, and Transgender (LGBT) parade in London, Britain EPA London Pride 2017 Revellers take part in London Pride, the Lesbian, Gay, Bisexual, and Transgender (LGBT) parade in London EPA London Pride 2017 A woman from the homeless charity 'Crisis' takes part in London Pride, the Lesbian, Gay, Bisexual, and Transgender (LGBT) parade in London EPA London Pride 2017 Revellers wave their flags as they take part in London Pride, the Lesbian, Gay, Bisexual, and Transgender (LGBT) parade in London EPA London Pride 2017 A woman walks past a shop front decorated with the Pride flag colours Getty London Pride 2017 People ride a tube escalator decorated with the Pride flag colours Getty

The parade, taking a 1.4-mile route through the city, comes after what is believed to be the world's largest Pride festival, with over 100 events having taken place since Saturday 24 June.

The march is also marking 50 years since the Sexual Offences Act 1967, which decriminalised homosexuality in England and Wales.

As part of the annual Pride weekend, a rainbow flag will be projected on to the Palace of Westminster for the first time.

Lord Fowler, Speaker of the House of Lords, said the move will demonstrate the UK's support for those living in countries around the world where people are persecuted for being gay.

The large-scale event is taking place as the country's threat level remains at severe, with police warning people to be vigilant as they enjoy the celebrations.

The Metropolitan Police said it is involved in high visibility police patrols, including both armed and unarmed officers, as well as plain clothes officers.