The UK’s exit from the EU next March could be delayed to allow for further negotiations and the public to make the “final decision”, Tony Blair is to say.
As a longstanding critic of Brexit, the former prime minister will say talks are “drifting” and may have to continue beyond next March’s exit date.
Backing a vote on the final deal, Mr Blair will say people have a right to choose what Brexit “version” they want.
The Brexit date is now enshrined in law after the EU Withdrawal Bill’s passage.
Prime Minister Theresa May has insisted the UK will cease to be a member from 29 March 2019.
Extending the Article 50 process, the two-year legal framework under which the UK is leaving the EU, to allow for more talks would require the approval of the UK government and all 27 other EU members.
In a speech at the Chatham House think tank in London , Mr Blair will say the process is “drifting” and attack what he will claim is a lack of leadership from Mrs May and Jeremy Corbyn.
He will say the prime minister is “more hostage than leader” because of divisions in her party and the Labour leader is “neglecting to lead the fight”
“We should plan now for the possibility we need to extend the March 2019 deadline,” he will say.
“Presently, we are drifting… with no clear negotiating position, no resolution of the Northern Ireland question, still vaguely hoping Europe will allow us access to the single market without abiding by its rules, which it will never do.”
He will liken talk about the prospect of the UK leaving without an agreement – which several cabinet ministers have said must remain an option – to “holding a negotiation on the top floor of a high-rise building and ‘threatening’ to jump out of the window if our demands are not met”.
Making his most outspoken call yet for a referendum on the final deal, he will suggest that Parliament has to “assert itself” and pave the way for another vote.
“The people must make the final decision because only they have the right to decide what version of Brexit they want or whether in the light of all they now know they prefer to remain.”
Both Mrs May and Mr Corbyn have ruled out another vote, saying their task is to implement the wishes of the British people, who voted by a majority of 51.9% to 48.1% to leave in the 2016 referendum.