Boris Johnson was reeling from a shock by-election defeat amid warnings the Tories’ “Blue Wall” is crumbling.
The Lib Dems pulled off a stunning victory on Thursday and overturned an 18,000 majority in Chesham and Amersham to seize the Conservative stronghold in Bucks.
Candidate Sarah Green won by 8,028 votes in a bombshell result which will trigger questions for the Conservatives.
Lib Dem leader Sir Ed Davey, who visits the constituency this morning, warned the Tory leader that if the result were repeated across the south “dozens of Conservative seats will fall to the Liberal Democrats” at the next election.
He told BBC Radio 4: “There is a lot more dissatisfaction with Boris Johnson than the polls suggest.”
It comes amid reports Tory MPs with Lib Dems as their nearest rival are preparing to join up and pressure the PM not to take their constituencies for granted.
Sir Ed said: “This is a huge victory for the Liberal Democrats. The people of Chesham and Amersham have sent a shockwave through British politics.
“We were told it was impossible for any party to beat the Tories here in Buckinghamshire.
“We were told this seat was too safe and the Tories too strong.
“This Liberal Democrat win has proved them utterly wrong. Across the South, the Tory Blue Wall is beginning to crumble. Here and in great swathes of the country, only the Liberal Democrats can beat the Conservatives and breach their Blue Wall.
“Sarah Green will be a great local champion for the people of Chesham and Amersham, and the Liberal Democrats will be a strong voice for everyone who feels let down and taken for granted by this dreadful Tory Government.
“This amazing win will strengthen our fight to safeguard our precious natural environment and build a fairer, greener, more caring country.”
The ballot was triggered by the death of long-serving Tory Dame Cheryl Gillan in April. The seat had been Conservative ever since its creation in 1974.
But Lib Dems always believed they could snatch victory in the poll, campaigning on planning issues and opposing the HS2 railway which will carve through the constituency.
The result will worry Conservative strategists after the Prime Minister won the December 2019 general election by demolishing Labour’s Red Wall across the North and Midlands.
True-blue shire Tories have warned the party was neglecting its traditional voters.
The Lib Dems put the government’s controversial planning reforms at the centre of their campaign.