Tory grandee Michael Heseltine has said he will vote Liberal Democrat in next week’s European elections, warning his own party has become "infected by the virus of extremism".
Lord Heseltine, a minister under Margaret Thatcher, said he could not back a party “myopically focused on forcing through the biggest act of economic self-harm ever undertaken by a democratic government” by delivering Brexit.
It came as the Prime Minister pledged a “bold offer” for MPs ahead of the publication of Brexit legislation, in a bid to win an unlikely victory when her deal is put to the Commons for a fourth time at the start of June.
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Lord Heseltime told The Sunday Times that the need for an inclusive Tory party is "greater than ever", and warned: "The middle ground of politics is empty."
He said he would resist any attempt to force him out of his party, and suggested the only alternative to a no-deal Brexit or a "Marxist government" led by Labour's Jeremy Corbyn was a second EU referendum.
Ministers will begin discussions on Monday on a package of measures to be included in the forthcoming Withdrawal Agreement Bill (WAB) aimed at securing cross-party support.
The weekly meeting of the Cabinet on Tuesday will then consider plans for a series of "indicative votes" in the Commons to establish which proposals could command a majority in the House.
The WAB is expected to include new measures on protecting workers' rights, an issue where agreement with Labour was said to have been close.
However, cross-party talks with Labour collapsed on Friday, making a majority for the WAB at its second reading unlikely.
The legislation is expected to include provisions on future customs arrangements with the EU and on Northern Ireland, including the use of technology to avoid the need for border controls with the Republic.
It will not, however, seek to re-open the Withdrawal Agreement - which included the controversial Northern Ireland "backstop" - after the EU repeatedly made clear it could not be re-negotiated.
Writing in The Sunday Times, Mrs May said: "I still believe there is a majority in Parliament to be won for leaving with a deal.
"When the Withdrawal Agreement Bill comes before MPs, it will represent a new, bold offer to MPs across the House of Commons, with an improved package of measures that I believe can win new support.
"Whatever the outcome of any votes, I will not be simply asking MPs to think again. Instead I will ask them to look at a new and improved deal with fresh pairs of eyes - and to give it their support."
Regardless of how the vote on the WAB goes, Mrs May will then meet the chairman of the Tory backbench 1922 Committee, Sir Graham Brady, to agree a timetable to elect her successor as party leader, paving the way for her departure from No 10.
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Another defeat would almost certainly see a ratcheting up of demands for her to go immediately, amid intense frustration at her failure to deliver on the 2016 referendum result.
Nigel Evans, the executive secretary of the 1922, said: "You can watch the movie Titanic a hundred times, but I'm afraid the ship sinks every time.
"An increasing number of Conservative MPs - even those who voted for it a second or third time - are saying enough is enough."