London mayor Sadiq Khan has urged Theresa May to hold a second referendum on Brexit.
The former Labour MP for Tooting believes the British public should have the chance to change their minds on leaving the European Union.
Khan insisted that the Government left it too late to negotiate a proper deal in time for the March 2019 separation date.
He said there are now only two possible outcomes: a bad deal or 'no deal' at all.
Writing in the Observer, the staunch Remainer blamed the government's handling of the negotiations and said the threat to living standards, the economy and jobs was too great for voters not to have a say.
He suggested if a so-called People's Vote were to be held, an option to remain a member of the EU should be included on the ballot paper.
'This means a public vote on any Brexit deal obtained by the government, or a vote on a 'no-deal' Brexit if one is not secured, alongside the option of staying in the EU,' he wrote in the article.
'People didn't vote to leave the EU to make themselves poorer, to watch their businesses suffer, to have NHS wards understaffed, to see the police preparing for civil unrest or for our national security to be put at risk if our cooperation with the EU in the fight against terrorism is weakened.'
May has repeatedly ruled out holding a second referendum following the vote two years ago to leave the EU.
She says members of parliament will get to vote on whether to accept any final deal.
The intervention in favour of a second referendum from Khan will put more pressure on Labour leader Jeremy Corbyn to also support the second referendum idea.
Labour is due to start its four-day annual party conference in a week's time.