THERESA May is facing fresh speculation over how long she will continue in power after a series of Tory MPs raised criticisms about her leadership, with one accusing the party of “letting the country down” and another calling for May to “name a date” for her departure.

In an strongly-worded intervention, Heidi Allen urged the “old guard” in the Conservatives to “understand why we need to change” as she pointed to a number of embarrassing front page newspaper stories.

The development comes amid intense Tory infighting over Brexit and increasing discontent from within the Tories over May’s premiership.

Allen tweeted an image of the Sunday Times front page showing two negative articles, below the headline ‘Tories in turmoil’.

One was a report highlighting claims over a lobbying scandal on Brexit while another contained controversial claims over Defence Secretary Gavin Williamson – a likely future frontrunner for Tory leader.

Williamson said on Thursday that Russia could cause “thousands and thousands and thousands” of British citizens’ deaths by targeting the UK’s energy infrastructure in a cyberattack.

Yesterday it emerged the Foreign Office headed by Boris Johnson, another likely Tory leadership contender, had made a complaint about the “tone” of the interview.

Allen drew attention to the stories, and tweeted: “And yet the old guard hangs on in and doesn’t understand why we need to change, saying MPs like me aren’t ‘proper Torys.’ [sic]”

She added: “Good God we need to get a grip and lead. We are letting this country down.”

Tory discontent over May’s leadership and Brexit has led to reports that the number of MPs who have written to the backbench 1922 Committee calling for a contest is close to the trigger point needed to force a battle aimed at toppling the PM.

Grant Shapps, who led a botched coup attempt after May’s conference speech in October, urged the PM to name a date when she will stand down and warned more letters were being sent to the Committee at the weekend.

Meanwhile, normally loyal backbencher Nigel Mills said the PM has not delivered on her early promises to tackle “burning injustices” and that MPs are concerned about the Government’s lack of direction.

He told BBC Radio 4’s World At One: “I think the frustration is the Prime Minister had what I thought was exactly the right drive and the right belief when she first came into office and it’s hard to see exactly how we’re making progress on that.

“We need to show a sense of what our values are, where we’re going, where we want to get to, and if that timeframe has to be 18 months or two years to deliver something, well then that’s fine, we can explain why that is.

“But I think where people are perhaps just a little concerned is perhaps we don’t quite know what that direction is, what those policies are going to look like or where they’re going to perhaps come from in that situation.

As speculation continued over May’s future David Lidington, minister for the Cabinet Office, urged the Conservatives to “come together” and stop infighting. Meanwhile, backbencher Nadine Dorries, an ally of Johnson, said she could say “almost categorically” he was not behind briefings about Williamson.