Against some expectations, Theresa May has kept her promise not to seek an early general election. The Prime Minister prides herself on sticking to her word and a campaign would cost valuable Brexit negotiating time. But one factor has received little attention: the increasing threat posed to the Tories by the Liberal Democrats.

Last month, Conservative MPs from Cornwall and Devon urged May not to go to the country for fear they would lose their seats. In Richmond, Tim Farron's party overturned Zac Goldsmith's 23,015 majority by attracting Remain voters and the Lib Dems have won 34 council seats from the Tories since May 2015.

The MPs' fears, I can reveal, were later reinforced by private Conservative polling. According to multiple sources, a survey conducted by Crosby Textor showed the party would lose most of the 27 gains they made from the Lib Dems in 2015, including all those in south London, all those in Cornwall and most of those in Devon. Lynton Crosby, who masterminded the party's general election triumph, is said to have personally told May of the grim findings. The Australian strategist's reappearance at CCHQ had encouraged speculation that the Prime Minister was preparing to seek an early contest. Tory MPs hope that by 2020, the scheduled date of the next election, the anger felt by Remain supporters at Brexit will have diminished.

Since their general election nadir, the Lib Dems have risen to double figures in national polling and now boast 87,000 members (more than double their low point under the coalition). Tim Farron told the New Statesman last week that only his party could deprive the Tories of their slim majority of 15 seats.

"The SNP cannot gain more than one seat off the Tories, so it can't be them ... Nobody, but nobody, thinks the Labour Party is in any position to make net gains from the Tories at all. So we are living with a Tory government for as long as we can see into the future, unless the Liberal Democrats, through our route, are able to bash the Tories to below a majority. That is the only plausible route at the moment, for Tories losing their majority.

"So I am doing progressive politics the biggest favour I can by strengthening my party, making it more attractive to people who are currently maybe Remain-voting, pro-market, moderate Conservatives, not for the protectionist wing."

A Conservative spokesman said he was unaware of the poll and that the party never comments on such matters.