European Commission President Jean-Claude Juncker | Frederick Florin/AFP via Getty Images British MEPs urge Juncker not to do a deal with Johnson Liberal Democrats say British PM has no mandate and UK election could reverse Brexit.

British Liberal Democrats in the European Parliament have a message for Jean-Claude Juncker: Stop trying so hard to reach a Brexit deal.

The European Commission president has promised to work day and night with U.K Prime Minister Boris Johnson and his negotiators to reach an agreement ahead of the October 31 deadline for the U.K.'s withdrawal.

But in a letter sent to Juncker by email on Friday, 16 British members of the European Parliament voiced dismay over a Sky News interview, to be broadcast in full this weekend, in which Juncker declared: "Brexit will happen" and "we can have a deal."

"We do not believe Brexit is inevitable," the MEPs told Juncker, "and neither should you."

The MEPs accused Johnson of trampling on democracy by suspending the British parliament, and said that because Johnson lacks a majority in the House of Commons, the EU should feel no obligation to help him reach a deal.

Rather, they urged Juncker to side with those British citizens hoping to stop Brexit and remain in the EU, and to hold out for a general election that might remove Johnson's Conservative Party from power. They also reiterated that the Liberal Democrats pledged to cancel Brexit if they win power.

"As 16 Liberal Democrat members of the European Parliament, elected with a clear mandate to stop Brexit and remain in the European Union, we wish to remind you that there are millions of pro-European UK citizens who are fighting for an alternative to Brexit," they wrote in the letter, a copy of which was obtained by POLITICO.

"While we understand that, for the time being at least, you have no choice but to negotiate with representatives of Prime Minister Johnson’s administration, we would remind you that Johnson leads an unstable minority Government," they wrote. "He therefore lacks a clear democratic mandate to negotiate Brexit on behalf of the U.K."

One of the MEPs who signed the letter, Luisa Porritt, went further, saying that the Commission chief's persistence in trying to reach a deal with Johnson represented precisely the sort of interference in British domestic politics that Juncker and other EU27 officials have long said they wanted to avoid.

"Why is it not interference for them to be saying Brexit has to happen, it's inevitable and there has to be a deal?" Porritt said in an interview. "That would be determining the path the U.K. has to take when there's an ongoing process here."

"It's right, I think, to stand back and respect that democratic process in the U.K. and let it play out," she said. "There's a good chance we'll have an election very soon and end up with a pro-European government."

In their letter, the MEPs told Juncker the EU should not help Johnson save his own political skin by reaching a last-minute deal.

"The British Prime Minister has resorted to shutting down British democracy in an attempt to force through Brexit," they wrote. "It would be a mistake for the European institutions to reward this authoritarian behaviour. What kind of message would that send to other populists with autocratic tendencies who are seeking to undermine liberal democracy across Europe?"

The MEPs apologized to Juncker that the U.K. had become such a headache for Brussels, but they also warned that a deal with Johnson could not be relied upon to settle the Brexit mess.

"Please do not fall into the trap of thinking that compromising with Boris Johnson now will in any way 'solve' the British relationship with Europe — or that you must agree a deal to avoid a disastrous 'no deal' outcome," they wrote. "As you know, the U.K. Parliament has legislated to ensure that the Government cannot crash the U.K. out of the EU without a deal."

Juncker’s spokeswoman, Mina Andreeva, said the Commission had no choice but to negotiate with Johnson in hopes of avoiding a catastrophic no-deal departure, and in accordance with a negotiating mandate set by the heads of state and government on the European Council.

“Brexit was never our choice. We did not want it. We regret it,” Andreeva said. “We believe an orderly withdrawal is better than a no-deal scenario.”

She added, “As far as we are concerned, the U.K. is leaving on 31 October. We have no choice but to try our best to reach a deal. President Juncker has been clear that he wants a deal. But not a deal at any costs. Any deal will need to be in full respect of our principles.”

The Commission has said many times that it can only negotiate with the prime minister as the representative of the U.K. government and that the EU respects the outcome of the 2016 referendum.

But Porritt said Brussels should recognize that many of those voters seem to be changing their minds, and that Johnson had neither a mandate in the British parliament nor among U.K. voters as a whole since he was appointed following the resignation of Theresa May and had not campaigned in a national election as Tory leader.

"Why are they working with him to help him get what he wants and shore up his tenure as prime minister?" Porritt asked. "What Boris Johnson is saying is not representative either of our parliament as a whole and what the MPs in parliament have been elected to do ... and it's not necessarily representative of the views of the British people either."

She added, "I would be wrong for people involved in the negotiations to just because there is a bit of Brexit fatigue settling in, to cave in and offer something to Boris Johnson at the 11th hour."

In their letter, the 16 MEPs pleaded for Juncker's help.

"We feel greatly ashamed of the fact that for so many years, you have had to deal with consecutive British Prime Ministers who have undermined the EU and the U.K.'s role within it," they wrote. "On behalf of the millions of pro-Europeans we represent in the UK, we ask for your patience and support at this difficult time for our country."

They added, "Those of us who support Europe also need Europe's support."