Liberal Democrat leader Sir Ed Davey said his party was now back in its former West Country stronghold after overturning a majority of more than 19,000 to win the Somerton and Frome by-election.

Until the 2015 electoral disaster following the coalition years, the South West had been a heartland for the Lib Dems and Sir Ed said the stunning result – which saw a 29.0 percentage point swing from the Tories – showed they could be a force there again.

The Lib Dems lost the Somerset seat in 2015 but Sarah Dyke won it back with a majority of 11,008 in the contest triggered by David Warburton’s resignation after he admitted cocaine use.

Sir Ed said: “This stunning victory shows the Liberal Democrats are firmly back in the West Country.

“Sarah Dyke will be an incredible local champion for the people of Somerset who have been neglected for far too long.

“She will fight for stronger local health services, better access to GPs and a fair deal for rural communities during this cost-of-living crisis.

“The people of Somerton and Frome have spoken for the rest of the country who are fed up with Rishi Sunak’s out-of-touch Conservative government.”

Sir Ed became the first Lib Dem leader since Paddy Ashdown in the 1990s to win four by-elections.

The victory in the Somerset seat follows the Tiverton and Honiton win in Devon last year and gains across the two counties in local elections.

Ms Dyke said she was “excited, exhilarated and most of all humbled” at the result.

She told reporters afterwards: “It’s unbelievable and most of all I am delighted that Somerton and Frome have finally got a voice in the constituency, but also in Parliament, and I can’t wait to get started.

“I think the result here shows a very clear message now that the Liberal Democrats are back in the West Country.

“Not only do we have the largest group of Liberal Democrat councillors on Somerset Council, we now have an MP in Somerset.

“We have a great legacy of Liberal Democrats MPs in Somerset. David Heath represented this constituency from 1997 to 2015 and the great, late Paddy Ashdown who was a hero to so many.”

As soon as the result was declared, defeated Conservative candidate Faye Purbrick left via a side entrance and got into a waiting car.

Reporters fired questions at her as she left the Bath and West of England Society showground.

Asked about the huge change in vote, she replied: “That would be something you would have to ask the voters.”

Asked if she had anything else to say, she added: “Thank you to everybody who voted for me – I really appreciate their support and I will be back.”