Sadiq Khan has said Article 50 should be revoked to “take away the panic” of leaving the EU on 31 October.
The London mayor also said the Labour party was the “party of remain” and that in any second referendum on Brexit it should campaign to stay in the EU.
Speaking to the BBC, Khan said: “Since December I’ve said what we we should do is is take away the panic, remove Article 50 to give us time to resolve negotiations with the EU to understand what we want.”
When asked whether this would mean cancelling Brexit altogether, Khan said the UK would then be able to re-serve Article 50 if the British public decided that wanted to leave the EU.
“The mistake made by Theresa May was serving a notice to quit before realising the terms of our exit,” he said.
“Nobody sensibly would serve notice to quit their accommodation before they’ve found new digs. Nobody would quit their job before they’ve found a new job.”
Khan’s intervention follows that of Labour’s deputy leader Tom Watson, who said earlier this week that Labour should campaign clearly for Remain.
“My experience on the doorstep tells me most of those who’ve deserted us over our Brexit policy did so with deep regret and would greatly prefer to come back; they just want us to take an unequivocal position that, whatever happens, we’ll fight to remain, and to sound like we mean it,” he said in a speech. “If we did it, we could win, whereas if we don’t, I fear we won’t.”
His remarks were rejected by Labour leader Jeremy Corbyn, whose position – agreed with trade unions – remains that Labour would negotiate a “credible” leave option which will be put on the ballot paper in a second referendum.