Theresa May should stand down next month, former Tory leader Iain Duncan Smith has said.

He made the call as the Prime Minister came under renewed pressure over Brexit, with new analysis showing the Tories are on course to lose almost 60 seats in the event of an election.

Meanwhile, Tory grandees raised the prospect of changing internal party rules to allow a fresh leadership challenge against Mrs May before the end of the year.

Mr Duncan Smith warned the Prime Minister faces a growing grassroots revolt over the UK’s failure to leave the EU and over plans to contest European elections. 

He told Sky News’ Sophy Ridge On Sunday: “I know that the Prime Minister has already said she’s going. She said she would go as and when the agreement was ratified which was looking at around about May, June. I think those dates still stand.

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“I think that what the Prime Minister has to do is aim everything now towards departure before the Euros [elections] which would then allow her to step away having done what she said she would do – get the UK out of the European Union one way or the other and then we can have another leadership election and pick a new leader, which is the way it has to be.”

He said the Tories’ poll ratings had started to crash after the UK failed to leave the EU on March 29.
An Electoral Calculus poll of polls for the Sunday Telegraph found the Tories risk losing 59 seats in the event of a general election – with Mr Duncan Smith among those facing being voted out. 
This would leave Labour as the largest party in the Commons.

Meanwhile, two former chairmen of the 1922 Committee of backbench Tory MPs said the party’s rules could be changed to allow a fresh leadership challenge. Under the current system, a move against the leader can only be brought once in a 12-month period.

Mrs May saw off a bid to oust her last December.

However, writing in the Sunday Telegraph, Lord Spicer and Lord Hamilton of Epsom said the 12-month rule on no-confidence votes could be altered. 

Graham Brady, chairman of the 1922 Committee, told the paper: “It is my understanding that the rules could in future be changed by the agreement of the 1922 executive.”

Read more: Labour MP David Lammy compares Tory Party's hard Brexiters to Nazis

But he added it was “less certain that it would be possible to change the rules during the current period of grace which was initiated with the triggering of a confidence vote on December 12 last year”.

It came as Cabinet Office Minister David Lidington, Mrs May’s de facto deputy, said talks between the Government and Labour aimed at finding a Brexit compromise would continue this week.

He told BBC1’s The Andrew Marr Show: “I had a good, business-like meeting with [shadow chancellor] John McDonnell a couple of days ago, and what we have agreed is a programme of meetings next week on particular subjects with the ministers and shadow ministers concerned getting together to talk about things like environmental standards, like workers’ rights, like security relationships between the United Kingdom and the EU.

“And then we would hope to take stock of where we are as soon as Parliament gets back after the Easter recess. But I don’t think that this question can be allowed to drag out for much longer.”

Mr Lidington said the two sides are “testing out” each other’s ideas. He said: “As a Government, we have always made it clear that while we will do our best to try and reach a compromise with the main opposition party, it would mean compromise on both sides.

“If that doesn’t work then what we will want to move towards is to put before Parliament a set of options with a system for making a choice and Parliament actually having to come to a preferred option, rather than voting against everything.

“Government said we will stand ready to implement what Parliament decides.”

Elsewhere, Labour leader Jeremy Corbyn came under renewed pressure to explicitly back a second EU referendum. 

Richard Corbett, Labour’s leader in the European Parliament, said the party risked haemorrhaging anti-Brexit voters unless it included a second vote in its manifesto for next month’s European elections.

Labour has repeatedly said it is keeping the option of another referendum on the table, but has attracted criticism over a perceived lack of commitment.