British Prime Minister Boris Johnson's Conservatives lost control of a parliamentary seat they dominated for nearly 200 years on Friday in vote that showed public dismay over a litany of scandals and stepped up pressure on him from mutinous lawmakers.

The defeat was described as "a kicking" for his Conservative Party, substantiating the fears among some that its reputation and electoral prospects are now suffering under Johnson.

The centrist Liberal Democrat candidate, Helen Morgan, won the North Shropshire seat by nearly 6,000 votes, overturning a 23,000-vote Conservative majority from 2019.

"Tonight, the people of North Shropshire have spoken on behalf of the British people. They have said loudly and clearly, 'Boris Johnson, the party is over'," Morgan said in her victory speech.

"Your government, run on lies and bluster, will be held accountable. It will be scrutinised, it will be challenged and it can and will be defeated."

The Conservatives had won every previous election for the mostly rural area of central England since the constituency was created in its current form in 1983. Conservative lawmakers have been dominant in the region for nearly 200 years.

The huge swing comes as Johnson, a 57-year-old former journalist who won a large majority in a 2019 election on a promise to "get Brexit done", faces criticism on several fronts, including over reports his staff held parties last Christmas when the country was in a COVID-19 lockdown. 

"Voters in North Shropshire were fed up and they gave us a kicking and I think they wanted to send us a message," Conservative chairman Oliver Dowden told Sky News. "We've heard that loud and clear."

However, Dowden said Johnson was still an asset and would lead the Conservatives at the next election, due in 2024.

Opinion polls show Conservatives falling behind their main rivals, the Labour Party, following an outcry over lawmakers' second jobs, criticism of the way Johnson funded the lavish refurbishment of his flat, and a surge in COVID-19 cases.