Video report by ITV News Europe Editor James Mates
Theresa May says the Conservative government will not permit a second referendum on Brexit.
Speaking outside the informal summit in Salzburg, Mrs May explained how the British public would not be allowed to vote again on the country's relationship with European Union, despite growing calls for another referendum.
Mayor of London Sadiq Khan is a vocal critic of Brexit process and this weekend said the final deal should be referred to the public to vote on.
"There are prominent Labour members like the Mayor of London who are now trying to take us back to square one and are backing a second referendum and postponing the Brexit day.
"I want to be absolutely clear, this government will never accept a second referendum.
"The British people voted to leave the European Union and we will be leaving on March 29, 2019.
"I now call on the Labour leadership to rule out a second referendum and stop trying to frustrate the Brexit process."
She added: "We held a people's vote - it was the referendum in 2016. People voted to leave the European Union, it is now a matter of trust in politicians that we should deliver on the vote of the British people."
Mrs May also said Chequers was “the only credible and negotiable plan on the table that delivers no hard border in Northern Ireland and also delivers on the vote of the British people”.
She added: “If we are going to achieve a successful conclusion then, just as the UK has evolved its position, the EU will need to evolve its position too.”
European Council president Donald Tusk, however, said the Prime Minister’s Chequers blueprint was a “welcome evolution” in the UK’s approach but major issues remained to be resolved including avoiding a hard border in Ireland and the future trading relationship between Britain and the EU.
The informal EU summit in Salzburg is the first time the continent's leaders have met together since Mrs May published her Chequers blueprint for Brexit in July.
The Prime Minister is expected to brief the other 27 leaders on proposals over dinner on Wednesday and they will then have a separate discussion on Thursday after she has left.
Brexit Secretary Dominic Raab said the UK's withdrawal plan was "ambitious" and "pragmatic", and urged the European Union to compromise.
He told radio station LBC that "we now need the EU side to move in our direction", adding: "I think the opportunity is there for the PM to explain, spell out, why it is a win-win deal, good for Britain, good for the EU.
"But also the fact that if we didn't get that movement, it would be lose-lose for the EU and the UK."
Mr Raab echoed Mrs May in dismissing a second referendum, saying it was "a mistake to bandy this around" and might harm negotiations with the EU.
He told LBC that another public vote would leave people thinking democracy was not being respected.
He added: "Even more important, as we go into these negotiations, if we said we were going to have a second referendum on the outcome we'd be inviting the EU to offer us the worst terms."
Video report by ITV News political correspondent Libby Wiener
German Chancellor Angela Merkel said in Salzburg: "I wish for a Brexit that will happen in a good atmosphere, in great respect for each other and that in certain areas a very very close cooperation remains possible – the areas of security both interior and exterior."