Boris Johnson’s Tories suffered a humiliating by-election defeat as the Liberal Democrats scored a stunning win in Chesham and Amersham.

Lib Dem Sarah Green became the country’s newest MP after winning a seat which had been a rock solid Tory bastion since its creation 47 years ago.

Party leader Sir Ed Davey said the result sent a “shockwave through British politics” by showing that the “Blue Wall” of Tory southern seats could be taken.

The prime minister had personally campaigned in the seat and a raft of cabinet ministers had visited it to try and boost the vote, but all to no avail.

The Tories claimed 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.

Johnson described claims that the Tories were neglecting the south in favour of so-called “red wall” former Labour seats in the north as “peculiar” and “bizarre”.

The contest 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 with a swing of 25%, Green took 56.7% of the vote to secure a majority of 8,028 over the second-placed Tories.

“This Conservative Party has taken people across the country for granted for far too long,” Green said.

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.

In her acceptance speech new MP 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.”

She added: “We will continue the work of holding this government to account for letting Covid rip through the care homes.

“We will speak up for the three million people excluded from financial support throughout the pandemic and we will challenge Boris Johnson to be far more ambitious in tackling climate change, supporting our frontline workers and backing our small businesses.”

The scale of the defeat will ring alarm bells in Conservative Campaign Headquarters (CCHQ).

One Tory source had told HuffPost UK  that the party was “sh*tting bricks” over possible loss of the seat. On the day of the by-election on Thursday, former PM Theresa May was knocking on doors in a desperate attempt to turn voters out, sources said.

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

Davey said that a key issue was the Tories were “taking people for granted” across the South.

But pollsters and experts also believe the Lib Dem victory shows the Tories are losing their well-off traditional voters as they focus on cementing gains in the largely Brexit-supporting “red wall” former Labour working class areas.

Lib Dem MP Munira Wilson told HuffPost UK’s Commons People podcast: “The Tories are now so focused on the red wall and their culture wars that I think really appeal and resonate in those [red wall] seats, that many of those people who, yes, largely voted Remain in the referendum… are looking for an alternative.”

“Things like the cut in foreign aid, which I see as part of that culture war,” Wilson said.

“Ministers will tell us, well actually it’s really popular and people want us spending that money in the left behind areas.

“In these sorts of areas [like Chesham and Amersham] I don’t think it’s an ‘either/or’, it’s an ‘and’- we have a moral obligation to be spending the 0.7% on foreign aid and looking after the world’s poorest, but equally investing in our recovery up and down the country.”

Wilson added that other cultural issues, like Tory MPs backing those who boo England football team for ‘taking the knee’, could play a part.

“I think the recent debacle over footballers taking the knee, for most people it’s like, you know, England’s in the Euros, we’re hosting loads of the matches, we should be getting behind our team and not suddenly criticising them for taking the knee.

“Lots of people in these seats recognise that there is still an issue with racism in many parts of our society and we should be doing everything we can to combat that.”

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

He added: “It’s an absolutely extraordinary result which must take into account the fact that the Liberal Democrat party didn’t just throw the kitchen sink at this constituency, I think it was the microwave, the table, the oven, the dishwasher, the dog, the cat and anything else that was lying around as well.“

Johnson attempted to play down the significance of the result, suggesting local issues came to the fore during the by-election.

“There were particular circumstances there and we are getting on with delivering our agenda for the whole country, that’s what one nation Conservatism is all about,” the PM said.

“We believe in uniting and levelling up within regions and across the country.”

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 source at Conservative Campaign Headquarters said “by-elections are always difficult for the governing party, particularly 11 years into government”.

But this did not stop the Tories winning Hartlepool from Labour in May, and the source acknowledged “there is no getting away from the fact this is a very disappointing result”.

The full result was:

Carolyne Culver (Green) 1,480
Brendan Donnelly (Rejoin EU) 101
Peter Fleet (Conservative) 13,489
Sarah Green (Liberal Democrats) 21,517
Carla Gregory (Breakthrough) 197
Adrian Oliver (Freedom Alliance) 134
Natasha Pantelic (Labour) 622
Alex Wilson (Reform UK) 414