The international trade secretary said he can only be “100 per cent certain” of Britain leaving the European Union if MPs support the prime minister in the crucial vote – scheduled for the week beginning the 14 January.
It follows Ms May’s decision earlier this month to pull the vote in the face of near-certain defeat and attempt to seek assurances from the EU to ease the concerns of rebellious backbench MPs over the Irish backstop.
Warning that failing to pass the deal would be “incendiary”, Mr Fox also told his colleagues that it is a “matter of honour” for them to support Ms May.
Speaking to The The Sunday Times, he said: “If we were not to vote for that, I’m not sure I would give it much more than 50-50.”
Having given the public the right to decide on EU membership in a referendum, “parliament cannot now, with any honour, renege on that result”, he added.
“Were they to do so, I think you would shatter the bond of trust between the electorate and parliament. And I think that would put us into unprecedented territory with unknowable consequences.”
His remarks came as The Observer reported that cross-party MPs are preparing to force the government to delay Brexit in order to avoid a no-deal scenario.
One senior Tory told the newspaper: “I have had these discussions with ministers. They will not say so in public but of course the option of a delay has to be looked at in detail now.
“If we are determined to avoid a no deal, and the prime minister’s deal fails, we will have to stop the clock, and that will give us time to decide to go whatever way decide thereafter.”
Jean Claude-Junker, the president of the European Commission, also told the German newspaper Welt am Sonntag that it was “entirely unreasonable for parts of the British public to believe that it is for the EU alone to propose a solution for all future British problems”.
He said: “My appeal is this: get your act together and then tell us what you want. Our proposed solutions have been on the table for months.”
Mr Juncker said it was up to the British to decide if the final decision is put back to the people in a second referendum or so-called people’s vote.
However, he said he was “working on the assumption that [the UK) will leave, because that is what the people of the United Kingdom have decided”.
“I have the impression that the majority of British MPs deeply distrust both the EU and Mrs May,” Mr Juncker added.
“It is being insinuated that our aim is to keep the United Kingdom in the EU by all possible means. That is not our intention.”
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