Speaking in Romania, Mr. Juncker also urged MPs to back the withdrawal deal because a no-deal Brexit would be a “disaster” for the United Kingdom. Mrs. May has held a number of discussions with the EU Commission President in order to deliver assurances to MPs that the controversial Irish backstop will not be used by the European Union to hold Britain hostage in a customs union.
The Prime Minister still faces stiff opposition to her deal from her parliamentary allies in the Democratic Unionist Party as well as backbench Tory MPs, who are expected to hand the 585-page withdrawal defeat a significant defeat when the House of Commons votes on it next week.
EU and British officials are working on potential clarifications, which set out the backstop is only a “temporary measure”, but it is unclear whether they will materialise ahead of the vote.
Mr. Juncker has warned Mrs. May and Brexiteers that any contacts in the days before the vote should not be considered as renegotiations, with the EU maintaining the withdrawal agreement is the “best and only deal possible”.
The eurocrat said: “We’ve said clearly that there can’t be renegotiation. There can be clarifications but that’s all.“We are discussing with Downing Street what these can amount to. But they can't be confused with renegotiation, especially regarding the backstop."
He added: “I do not like the prospect of a no-deal, which would be a disaster for our British friends.
“Every effort needs to be made to make sure this important issue is resolved satisfactorily.”
Mr. Juncker also backed Romania, the current incumbent of the EU’s rotating presidency, to oversee Britain’s departure from the bloc.
He said: “The United Kingdom will leave the EU at the end of March 2019 and so the Romanian presidency, with elegance and wisdom, will have to act in this difficult period after Brexit, but I have every confidence in you to manage in a remarkable way this phase which is a difficult phase.
“To me, the departure from the United Kingdom is a tragic event that Europe does not need, but there is a democracy and we can not prevent a country that wants to leave to actually leave us, but we will certainly not be happy on March 30.”
But uncertainty still surrounds Britain’s EU divorce as MPs in Westminster continue to expose the growing divides among them despite British voters opting to leave in the 2016 EU referendum.
According to BBC research, Mrs. May could suffer the biggest Commons defeat on record when MPs vote on her Brexit deal.
The broadcaster expects as many as 433 MPs to oppose the deal while only 206 side with the Prime Minister to guarantee the UK leaves on her agreed terms on March 29.
In the face of the defeat, Mrs. May will no longer be able to simply allow Britain to leave the EU without a deal after a series of Commons defeats this week, which Jeremy Hunt claims have made staying in the bloc more likely.
The Foreign Secretary told the BBC: “The parliamentary arithmetic is challenging. But, also, the choices are very clear. And I think after this week things have changed.
“Up till now I think people have quite rightly been worrying about the prospects of no deal. Now there is another possibility coming into sight, which is actually no Brexit.
“And why is that? We have a government that is committed to delivering Brexit. But it doesn’t have a majority.”
He added: “If this deal is rejected, ultimately what we may end up with is not a different type of Brexit but Brexit paralysis. And Brexit paralysis ultimately could lead to no Brexit.
"I’m saying this would be an incredibly damaging breach of trust and it would also be very bad for Britain’s reputation abroad, having decided to leave the EU, if we in the end for whatever reasons found we weren’t able to do it.
"If we were, as a political class, not to deliver Brexit, that would be a fundamental breach of trust between the people and the politicians. I think that is something that we would regret for many, many generations."
