European Council President Donald Tusk said in an interview on Friday that he believes there may still be a "20-30%" chance that Britain remains in the European Union.
Speaking with Polish daily Gazeta Wyborcza, he said that if a 2016 referendum can reverse a decision made in 1975, it should be possible to hold a second Brexit vote.
Tusk was referring to the time Britons voted on whether they wanted to remain in what, 44 years ago, was the European Economic Community.
The president stressed that it was perhaps unfair to the British people that the major consequences of their vote were not made clear until after the June 2016 ballot.
"The real debate on the consequences of Brexit started not before or during the referendum campaign, but after the vote. Today the results would probably look different," said Tusk.
Brexit 'triggered a pro-Europe movement'
"Paradoxically it is Brexit that triggered a pro-European movement in the UK," he added. "Today, chances that there will be no Brexit are at 20-30%. That's a lot."
Tusk said he was uncertain how Britain could expect to leave the EU by the new deadline of October 31, when Prime Minister Theresa May's withdrawal agreement has already been rejected by parliament three times.
"Month by month it is becoming clearer that the UK's departure from the EU will look completely different to what the Brexit promoters had (forecast)," he told the Gazeta Wyborcza, declaring that he would never give up hope that the UK would reverse course.
The European Court of Justice (ECJ) has ruled that Britain can unilaterally stop Brexit without seeking approval from EU member states.
As a result of the decision to extend the deadline, the UK will participate in EU elections at the end of May.