Theresa May’s Brexit deal is “doomed” and must be renegotiated, ex-defence secretary Sir Michael Fallon has said.
Sir Michael launched a scathing attack on the proposed EU agreement, saying it was the “worst of all worlds”.
Asked whether Mrs May should stay on as Tory leader if it was rejected by MPs, he said it was “up to my colleagues”.
The BBC’s Laura Kuenssberg said he was “not one of the usual suspects” on Europe and his remarks showed the depth of Conservative opposition to the deal.
Parliament will vote on whether to accept or reject the terms of the UK’s withdrawal and future relations negotiated by Mrs May on 11 December.
Sir Michael’s decision to come out against the deal is a blow to Mrs May, who is struggling to muster support in Parliament for it.
The veteran Conservative MP, who served as defence secretary under David Cameron and Theresa May before having to resign a year ago, told MPs on Monday the agreement was a “huge gamble” as it would see the UK give up its power to influence EU rules and regulations in return for vague assurances over future trade arrangements.
He told BBC Radio 4’s Today that “this is not a good deal and we need a better deal”.
“My fear is that this deal gives us the worst of all worlds,” he said. “No guarantee of smooth trade in the future and no ability to reduce the tariffs that we need to conclude trade deals with the rest of the world.
“So, unless the House of Commons can be persuaded somehow that those are possible then I think, yes, the deal is doomed.”
Asked if Mrs May was also doomed, he replied “that’s up to my colleagues”, while stressing that a change of leader would not necessarily address the difficulties the UK now found itself in.
When it was put to him that did not sound like an endorsement of Mrs May he said “take it anyway you want”.
The prime minister is continuing to making the case for the agreement, which she says delivers on the 2016 referendum vote and is in the national interest.
During visits to Wales and Northern Ireland later, she will argue that it gives certainty to farmers and other businesses.