Tory MPs voted in large numbers in the House of Commons against delaying Brexit again until even 30 June, though Ms May is set to be forced into a much longer extension.
Cabinet members Andrea Leadsom and Liam Fox, along with transport secretary Chris Grayling, attorney general Geoffrey Cox and party chair Brandon Lewis all failed to positively back the government’s approach.
Earlier Ms Leadsom publicly voiced her desire for the government to renegotiate Britain’s withdrawal agreement instead, something Ms May has repeatedly said cannot happen.
In a leaked letter to Tory MPs international trade secretary Dr Fox also poured scorn on the idea of Britain remaining in a customs union with the EU, something which other ministers concede is the likely outcome of cross-party talks with Labour to find a deal that can win a Commons majority.
The cross-party talks closed on Tuesday without having yet reached agreement but with both sides saying they are committed to doing a deal and agreeing to meet again in two days.
Following previous decisions by MPs, the government was forced to put Ms May’s request for an extension to the Article 50 negotiating period to a vote in the Commons.
While Ms May’s plan to extend until 30 June was approved by a majority, 97 Tory MPs voted against it – demonstrating the deep splits over her approach and her ever-diminishing authority.
Earlier in the day Brexiteer backbenchers vowed that the UK would sabotage European projects from inside the EU if Brexit does not happen, warned that Brussels “will be facing perfidious Albion on speed” and called for the removal of Ms May as prime minister.
Ahead of the prime minister’s meeting with German chancellor Angela Merkel on Tuesday, leader of the Commons Ms Leadsom urged her to ask for the withdrawal agreement to be reopened – an idea the government has abandoned.
Ms Leadsom told ITV News: “The prime minister is off to see Angela Merkel today and it would be fantastic if Angela Merkel will try to support a proper UK Brexit by agreeing to reopen the withdrawal agreement.”
But Ms May’s official spokesman dismissed the idea, telling reporters: “Any plan going forward would be based on the current withdrawal agreement.”
Soon after the comments, other members of the prime minister’s cabinet continued talks with Labour to try and find a compromise deal, including her deputy David Lidington, chancellor Philip Hammond, Brexit secretary Steve Barclay, environment secretary Michael Gove, and business secretary Greg Clark.
Labour is said to have demanded a customs union and is under pressure to also secure a confirmatory referendum on anything which is agreed.
But in a clear sign of intensely strained party unity, Dr Fox sent a letter to the chair of the Tory backbench 1922 Committee setting out in detail his opposition to a post-Brexit customs union.
The letter warned it would leave the UK unable to set its own trade policy but forced to open its markets to any country with which the EU struck a free trade agreement.
He went on: “In such a scenario the UK would have a new role in the global trading system – we ourselves would be traded.
“As the famous saying in Brussels goes, if you are not at the table, you are on the menu.”
Negotiating teams from the government and Labour began their talks over an informal lunch of sandwiches, sausage rolls, onion bhajis, a fruit platter and biscuits.
After three hours Labour’s negotiating team left, with shadow business secretary Rebecca Long-Bailey saying: “We’ve had really constructive discussions today and covered a number of issues in great detail.
“There’s not really been any fundamental shift or a change in position of the deal itself. But we’re hopeful that progress will be made.”
Shadow chancellor John McDonnell said earlier that Labour was actively seeking a way to stop a Brexit deal between the parties being unpicked by a future Tory leader like Boris Johnson.
Mr Gove also said there had been “constructive” discussions, but added: “There are number of issues where we differ, but we are anxious to ensure that we can carry on with this process.”
More talks are planned for Thursday, when Ms May is due to return from an emergency European Council summit where EU leaders are expected to dismiss her request for a short delay to Brexit until June and keep Britain in until the end of the year.
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