Tony Blair has warned voters that time is running out to reverse Brexit.
The former British Prime Minister says the break with Brussels will torpedo Britain's remaining clout and be regretted for generations to come.
Both opponents and supporters of Brexit agree that the divorce is Britain's most significant geopolitical move since the Second World War.
However, they disagree on the post-Brexit future for the UK economy and its relation with the world's biggest trading bloc.
Is Tony Blair usually this outspoken?
No. But he has become increasingly so about Brexit.
He implored his Labour Party, which is now led by socialist Jeremy Corbyn, to join the fight to stop Brexit.
What has Blair said?
That Britain would be poorer and weaker after it breaks with Brussels. He warns that UK Prime Minister Theresa May has solved none of the problems over Northern Ireland's post-Brexit status.
"We are making an error the contemporary world cannot understand and the generations of the future will not forgive," Blair said in an article published on his website.
"2018 will be the last chance to secure a say on whether the new relationship proposed with Europe is better than the existing one," the 64-year-old added.
"Make Brexit the Tory Brexit. Make them own it 100 percent," Blair said. "If Labour continues to go along with Brexit and insists on leaving the Single Market, the handmaiden of Brexit will have been the timidity of Labour."
Blair has repeatedly called for Brexit to be reversed, echoing other opponents of Brexit such as French President Emmanuel Macron and billionaire investor George Soros. They have suggested Britain could still change its mind.
And is the support for this from the public?
Some, although so far, opinion polls show little sign of a complete change of heart. It is unclear how Brexit could be stopped of both major political parties officially support the divorce.
Half of Britons support a second vote on whether to leave the European Union and a majority think the government may be paying too much money to the EU to open the way to trade talks, according to an opinion poll published last month.
Does Blair have influence?
The former prime minister is unpopular in Britain for his decision to back the then-US President George W.Bush's 2003 invasion of Iraq and the justification he used for going into a war that cost the deaths of 150.000 Iraqi civilians and 179 British soldiers.
What do Brexit supporters say?
They have dismissed his comments and have accused him of undermining both the British negotiation and the will of the people.
"Blair and his elitist gang are damaging oru negotiating strength, thus damaging our national interest by their continuing efforts to undermine democracy," said Richard Tice, who helped found one of the two Leave campaign groups.
"History will not forgive them."
Brexit - what you need to know
More than a year-and-a-half since the 2016 Brexit vote, the UK remains deeply divided over the planned EU exit
Prime Minister Theresa May says it will take place on March 29, 2019
Leaving the European Union was once far-fetched: just over 15 years ago, British leaders such as Blair were arguing about when to join the euro, and talk of an EU exit was the reserve of sceptics on the fringes of both major parties.
But the turmoil of the euro zone crisis, fears in Britain about immigration and a series of miscalculations by former Prime Minister David Cameron prompted the United Kingdom to vote 52 to 48 percent for Brexit in a June 2016 referendum.