THERESA May dropped key elements of her plan for a softer Brexit yesterday amid mounting pressure from the hardline Eurosceptic wing of her party.

Over the weekend it emerged more than 100 Tory MPs had joined a WhatsApp group designed to thwart the Chequers proposals for closer EU alignment.

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There were calls, too, for former foreign secretary Boris Johnson to give a “Geoffrey Howe”-style resignation speech in the Commons, which could have led to a flood of letters to the 1922 committee, sparking a vote of no confidence and a leadership contest. Some 40 letters have been submitted to the committee’s chairman Graham Brady and just eight more could bring the vote about.

Keenly aware of how Howe’s speech set in train the events which brought about Margaret Thatcher’s demise as prime minister and Tory leader, May was no doubt anxious to prevent history from repeating itself.

Her concessions to the Brexiteers therefore see off a leadership challenge for now, but the autumn will bring huge new challenges.

In an interview with The Times yesterday Stewart Jackson, a former adviser to David Davis, who quit as Brexit secretary last week over the Chequers plan, suggested rebels may be gearing up for a contest later in the year. “It’s hard to judge where we will be in the autumn,” he said. “I think those of us who have been committed to delivering Brexit have a responsibility to say that the worst-case scenario could be that in October, faced with no deal and an intransigent EU, the Prime Minister will be in a cul de sac ... I think it’s going to be a quagmire in the autumn because there is no majority.”

Kirsty Hughes, director of the Scottish Centre on European Relations, said May’s concessions to the Brexiteers underlined the future difficulties she will have in getting her backbenchers to agree any deal reached with Brussels.

Hughes said: “She has temporarily got out of a Brexiteer rebellion by accepting their rebellion so to me it suggests she can’t get any likely deal with the EU past the backbenches.”

“It doesn’t mean she can’t get a deal with the EU but that there may be no deal that there is a majority for in the House of Commons.

“ If the Brexiteers keep intervening, saying you mustn’t agree this, you mustn’t do that, it either increases the changes of a no deal, or a deal that the backbenchers won’t vote for. It makes it all more of a mess and more likely to end up in crisis.”