The leader of the Liberal Democrats has said the party’s historic win in the Chesham and Amersham by-election will “send a shockwave through British politics”.

Sir Ed Davey claimed that the result demonstrates that the “Blue Wall” of Tory southern seats could be vulnerable after Boris Johnson’s Conservative Party suffered a humiliating defeat in the contest.

Liberal Democrat Sarah Green is the country’s newest MP after winning the Buckinghamshire seat, which had been a Conservative stronghold since its creation in 1974.

The Tories sought to limit the damage, insisting it was difficult for governing parties to win by-elections, but defeated candidate Peter Fleet acknowledged the Conservatives had to rebuild “trust and understanding” with voters.

Policing minister Kit Malthouse branded the defeat “very disappointing” and said that there would have to be a “fairly significant post-match analysis” on what went wrong for the Tories.

The by-election was triggered by the death of former Cabinet minister Dame Cheryl Gillan, who took the seat with a majority of 16,233 in the 2019 general election – some 55% of the vote.

In a stunning result, Ms Green took 56.7% of the vote to secure a majority of 8,028 over the second-placed Tories.

Sir Ed told BBC Breakfast on Friday: “I think this will send a shockwave through British politics.

“Liberal Democrats have had good wins in the past but this is our best ever by-election victory and it if was repeated across the South, literally dozens of Conservative seats would fall to the Liberal Democrats.

“People talked about the Red Wall in the North, but forgotten about the Blue Wall in the South, and that’s going to come tumbling down if this result is mimicked across this country.”

Chesham & Amersham by-election result
(PA Graphics)

The Green Party came third with 1,480 votes, with Labour trailing in fourth with just 622 votes, losing the party’s deposit in the process.

Polling expert Sir John Curtice told BBC Radio 4’s Today programme that he made it the “worst Labour performance in any by-election” after it took just 1.6% of the vote.

In her acceptance speech, Ms Green said: “Tonight the voice of Chesham and Amersham is unmistakable. Together we have said: ‘Enough is enough, we will be heard, and this Government will listen.’

“This campaign has shown that no matter where you live, or how supposedly safe a constituency may appear to be, if you want a Liberal Democrat member of Parliament, you can have a Liberal Democrat Member of Parliament.”

The country’s newest MP and Sir Ed celebrated the triumph at a victory rally in the constituency on Friday, where the pair stood in front of a blue wall made of plastic bricks, which the leader then smashed with an orange hammer.

The scale of the defeat will have alarm bells ringing in Conservative Campaign Headquarters (CCHQ), but Mr Malthouse denied that the “Blue Wall” was now at stake.

The Conservative MP told BBC Radio 4’s Today programme: “We believe there is no red and blue, we believe there is one nation, and we’d like to win every seat we possibly can.

“I think the package that the Prime Minister is offering to the country as we come out of the pandemic will be attractive to people in Liverpool and Warrington and Darlington, as well as in Andover in my constituency.”

Major issues in the campaign included the HS2 rail line, which cuts through the constituency, and proposed planning reforms which have sparked fears about building in the countryside around the seat in the Chilterns.

Mr Fleet said: “Clearly this was a very disappointing result, not the result that I was expecting, nor my team.”

Tory chairwoman Amanda Milling said the “work starts now to show how it’s Conservatives that can deliver on the people’s priorities and regain their support”.

A Conservative source said: “By-elections are always difficult for the governing party, particularly 11 years into government, but there is no getting away from the fact this is a very disappointing result.”

The victory caught bookmakers off guard – the Tories were firm favourites and the Lib Dems closed at 4/1 with Ladbrokes.

“Fair to say this was a night for the punters,” the firm said on Twitter.