London Mayor Sadiq Khan today warned voters that "out is out" and that there would be no going back from a vote to leave the European Union.
Speaking alongside Labour Leader Jeremy Corbyn, First Minister of Wales Carwyn Jones AM and Leader of Scottish Labour, Kezia Dugdale MSP, at a Labour In for Britain event in Kings Cross, London, Mr Khan said that the outcome of the referendum was a decision that would affect the UK "for decades to come".
Urging the electorate to vote for the UK to remain in the EU, the former Labour MP warned: "This is the fight of our lives".
Mr Khan added that working together as part of the EU, the UK would be "stronger, safer, and better off".
London Mayor Sadiq Khan has met with Labour leader Jeremy Corbyn in public for the first time after a weekend of contrasting election fortunes.
While Mr Khan enjoyed electoral success in the capital, Mr Corbyn oversaw less encouraging results for his party in the UK's "Super Thursday" elections.
New London mayor Sadiq Khan has said that he felt disappointed by how the Conservative campaign was run during the mayoral election and referred to the tactics used as "nasty".
Speaking on the BBC's Andrew Marr show he said: "I was disappointed that the Conservative party chose to have a campaign that was nasty, that was negative and that was divisive."
Sadiq Khan's first public engagement since being installed as Mayor of London on Saturday will be at a Holocaust Remembrance Day ceremony.
Mr Khan will appear at the event in Barnet, north London, alongside a number of prominent figures in the Jewish community to commemorate the millions slaughtered during the Nazi genocide.
Up to six millions Jews are known to have been killed in the Holocaust during the Second World War.
The appearance comes after Mr Khan took a strong stance against anti-Semitism during the racism scandal which engulfed the Labour Party in recent weeks.
Newly elected London mayor Sadiq Khan has hailed the announcement that he had won the capital's mayoral race as a "victory for hope over fear and for unity over division".
In a message of thanks posted to supporters on his Twitter page in the early hours of Saturday morning, shortly after he broke the Conservatives' eight-year hold on City Hall, Khan also hailed the win as "an amazing victory".
He also linked to his website where his full message of thanks was printed:
An aide to Labour's London mayoral candidate Sadiq Khan has been suspended over a series of offensive messages posted on social media in 2012.
Shueb Salar, a parliamentary assistant to the former minister, posted several messages on Twitter containing abusive language about women and homosexuals.
A spokeswoman for Mr Khan said they were "serious issues" and Mr Salar had been suspended from the mayoral candidate's parliamentary office pending an investigation.
In one message, posted in May 2012, Mr Salar said "currently hating on all you faggots who have finished uni" while a message from April 2012 suggested that the way to "treat a lady" was to "buy her a nice iron and extend the kitchen for her".
Mr Salar started working for Mr Khan in his Westminster office in November 2014.
Cabinet minister Chris Grayling questioned Mr Khan's judgment in employing someone who had published the comments.
He said: "'These comments have absolutely no place in modern society. They raise serious questions about the judgement of Sadiq Khan who chose to employ this man despite his views being public, on a Twitter account followed by Khan himself."
An MP accused the government of trying to share a "best practice of how to behead" with Saudi Arabia after the Justice Secretary defended the Government's attempt to sell expertise to the country's prison service.
Shadow justice secretary Sadiq Khan slammed the MoJ bid for the £5.9 million contract.
Justice Secretary Chris Grayling defended the move, saying the Government has always tried to encourage "improvements" and "best practice" in countries around the world.
The pair clashed after reports that the MoJ's commercial arm, Just Solutions international, is hoping to sell its expertise to Saudi Arabia's prison service.
Government cuts could be behind half of convicted sex attackers, violent criminals and burglars avoiding prison sentences, Labour said.