Boris Johnson's slim majority shrinks to 1 after by-election defeat

Britain's new Prime Minister Boris Johnson's already slim parliamentary majority has been cut down further to just one with the loss of an MP to the anti-Brexit Liberal Democrat party in a by-election in Wales.

In one of his first major election clashes since taking over from Theresa May last month, Johnson's Conservative Party candidate lost the seat for the party in the Welsh constituency of Brecon and Radnorshire.

Liberal Democrat MP Jane Dodds overturned an 8,038 majority to beat incumbent Tory MP Chris Davies by 1,425 votes in results announced overnight on Thursday.

It was the first electoral test for Johnson just eight days after becoming the prime minister.

It is the quickest by-election defeat for any new prime minister since World War II, the BBC reported.

"My very first act as your new MP when I get to Westminster will be to find Mr Boris Johnson, wherever he's hiding, and tell him to stop playing with the future of our community and rule out a no-deal Brexit," said Dodds.

The by-election was a result of Davies being forced to stand again following a petition for him to be unseated after a conviction for a false expenses claim, which he had admitted to and fined for.

He was re-selected by the Tories to contest and win back the seat, showing confidence in him despite the mistake.

However, the loss leaves the Conservatives in an even more precarious position, having to already rely on the 10 Northern Irish Democratic Unionist Party (DUP) MPs for a working majority in the House of Commons.

May suffered repeatedly as a result of the slim majority and now her successor has the support of 320 MPs, including the DUP, while the Opposition parties have 319.

The new Liberal Democrat leader Jo Swinson called the latest win a "superb victory" as the party continues its campaign for a new referendum on Britain's exit from the European Union (EU).

"Boris Johnson's shrinking majority makes it clear that he has no mandate to crash us out of the EU," she said, celebrating the Liberal Democrats' 13th MP in the Commons.

Johnson won the Tory leadership contest with the pledge of taking the UK out of the 28-member economic bloc within the October 31 deadline, with or without a deal.

The deep divisions that exist on Brexit were laid bare in the by-election, which saw the Green Party and local Plaid Cymru backing the Liberal Demcocrats in an alliance by not fielding rival candidates in order to consolidate the anti-Brexit alliance.

The Labour Party, which came in fourth after the Nigel Farage led Brexit Party, blamed voters switching tactically to the Liberal Democrats.

The rather oddly named Monster Raving Loony Party managed to push the far-right UK Independence Party (UKIP) into sixth place.

The turnout was 59.6 per cent, down from 74.6 per cent at the 2017 General Election, but the highest for a by-election in the UK since 1997.