Andrea Leadsom, the Commons leader, has warned Theresa May that she will not accept a new Brexit plan that leaves open the possibility of a customs union, before a key cabinet meeting to finalise the proposals.
In a sign of the difficulties the prime minister faces in getting her withdrawal agreement bill (Wab) past her own ministers, let alone the Commons, Leadsom stressed that her backing was conditional.
“I continue to support the prime minister to get her withdrawal agreement bill through,” she told BBC Radio 4’s Today programme. “It is leaving the European Union, and so long as it continues to be leaving the European Union I continue to support it.”
Asked what she meant, Leadsom said that while she could support the customs arrangements already in the plan, any move to tempt Labour voters by holding open the possibility of a formal customs union, which could affect the UK’s ability to sign its own trade deals, would make it impossible for her to support it.
She said: “I have been very clear for years – leaving the EU means leaving the single market, leaving the customs union, taking back control of our money, border and laws.”
Such ultimatums by the minister tasked with guiding the legislation through the Commons highlights the uphill task May faces in finalising the plan and then presenting it to MPs in the week starting 3 June.
In another blow to the bill’s prospects, Jacob Rees-Mogg said he might not support it, having voted for the deal the last time. Speaking on Conservative Home’s Moggcast podcast, the leading backbench Brexiter said: “The reason for voting for it on the third go was so that we would leave broadly on time. That has been lost.
“Mrs May’s deal is a very bad deal so, as we have already delayed, it is hard to see any point in having a bill which fails to avoid the European elections, fails to get us out on time, fails to get the process going in the way that might have worked with a new leader coming in.”
Given May was due to quit, he said, the bill risked being “a weight round the neck of the new leader”.
Leadsom and other Brexiters will be pushing hard to avoid any concessions to Labour, especially after the health secretary, Matt Hancock, said the bill could be amended during its passage to include ideas such as a customs union or even a second referendum.
However, few Labour MPs are likely to be tempted to support it. The shadow foreign secretary, Emily Thornberry, said the vote on the Wab could be seen as a “political version of the last rites” for May’s time in No 10.
“From what I’ve heard there’s really no radical difference between this withdrawal agreement bill and Theresa May’s meaningful vote that she’s lost many times,” Thornberry told Today.
“I think that Labour MPs will vote against it, I think that Tory MPs will vote against it. And I’m afraid it’s almost a piece of political theatre, as if she needs to have a dignified way of leaving – it’s like her moment that she will resign when she doesn’t get this bill through.”
On the other side of the divide the chancellor, Philip Hammond, will battle to rule out a no-deal Brexit, something he will say in a speech on Tuesday evening is being pushed by “the populist right”.
He is to tell the CBI conference: “Let me remind them: the 2016 leave campaign was clear that we would leave with a deal. So to advocate for no deal is to hijack the result of the referendum and, in doing so, knowingly to inflict damage on our economy and our living standards.”
In an indication of the wider turmoil gripping the Conservatives, it emerged on Monday night that the former deputy prime minister Michael Heseltine had had the whip suspended after saying he would vote for the Liberal Democrats in Thursday’s European election.
The Wab is May’s fourth and final attempt to push her Brexit plan through the Commons. Now packaged as a formal bill rather than an outline plan, the prime minister has promised a “new, bold offer”.
Leadsom said this would include new guarantees on workers’ rights and environmental protections, and would “promote alternative arrangements” to the Irish backstop, a key demand of Tory Brexiters.
“All of those things will be attractive to many members across the house,” she said. “But what is absolutely key for me will be that it does deliver Brexit.”
Leadsom is among several ministers who will compete to succeed May when the prime minister steps down in the next few weeks. She told Today that if she became PM she would be willing to countenance a no-deal departure if the current plan failed to pass.
“For any negotiation to succeed you have to be prepared to walk away,” she said, “and the legal default position is that on 31 October the United Kingdom leaves the European Union without a deal.”