Boris Johnson has suffered a significant blow after the Liberal Democrats won the Brecon and Radnorshire by-election, slashing the new prime minister’s Commons majority to just one.

Jane Dodds, the Lib Dem candidate, overturned a Tory majority of 8,083 to defeat incumbent Chris Davies by 1,425 votes in the Welsh constituency.

The party chose to field Mr Davies as its candidate despite him being ousted in a recall petition by 19 per cent of the electorate in the Welsh seat, after he admitted submitting false claims for expenses.

The result further weakens Mr Johnson’s grip on the Commons and could make it harder for him to pass both his Brexit plan and his domestic agenda through parliament.

It also breathes fresh hope into the prospect of other “Remain alliances”, after Plaid Cymru and the Greens threw their weight behind the Lib Dems to prevent a split in the pro-EU vote.

Boris Johnson's cabinet: Who's in and who's out Show all 40 1 /40 Boris Johnson's cabinet: Who's in and who's out Boris Johnson's cabinet: Who's in and who's out In: Jacob Rees-Mogg Jacob Rees Mogg appointed Leader of the Commons AFP/Getty Boris Johnson's cabinet: Who's in and who's out In: Esther McVey Esther McVey appointed housing secretary AFP/Getty Boris Johnson's cabinet: Who's in and who's out In: Jo Johnson Jo Johnson appointed new business and energy secretary EPA Boris Johnson's cabinet: Who's in and who's out In: Brandon Lewis Brandon Lewis appointed immigration secretary Getty Boris Johnson's cabinet: Who's in and who's out In: James Cleverly James Cleverly appointed Conservative Party chairman PA Boris Johnson's cabinet: Who's in and who's out In: Baroness Evans Baroness Evans remains Leader of Lords PA Boris Johnson's cabinet: Who's in and who's out In: Julian Smith Julian Smith appointed Northern Irish secretary Reuters Boris Johnson's cabinet: Who's in and who's out In: Alister Jack Alister jack appointed Scottish secretary PA Boris Johnson's cabinet: Who's in and who's out In: Alun Cairns Alun Cairns remains Welsh secretary AFP/Getty Boris Johnson's cabinet: Who's in and who's out In: Grant Shapps Grant Shapps appointed transport secretary Getty Boris Johnson's cabinet: Who's in and who's out In: Alok Sharma Alok Sharma appointed international development secretary AFP/Getty Boris Johnson's cabinet: Who's in and who's out In: Robert Buckland Robert Buckland appointed justice secretary Getty Boris Johnson's cabinet: Who's in and who's out In: Amber Rudd Amber Rudd remains work and pensions secretary Getty Boris Johnson's cabinet: Who's in and who's out In: Robert Jenrick Robert Jenrick appointed housing and communities secretary AFP/Getty Boris Johnson's cabinet: Who's in and who's out In: Andrea Leadsom Andrea Leadsom appointed business secretary Reuters Boris Johnson's cabinet: Who's in and who's out In: Nicky Morgan Nicky Morgan appointed culture secretary Getty Boris Johnson's cabinet: Who's in and who's out In: Gavin Williamson Gavin Williamson appointed education secretary AFP/Getty Boris Johnson's cabinet: Who's in and who's out In: Theresa Villiers Theresa Villiers appointed environment secretary AFP/Getty Boris Johnson's cabinet: Who's in and who's out In: Liz Truss Liz Truss is appointed international trade secretary Reuters Boris Johnson's cabinet: Who's in and who's out In: Ben Wallace Ben Wallace appointed defence secretary EPA Boris Johnson's cabinet: Who's in and who's out In: Stephen Barclay Stephen Barclay remains EU secretary AFP/Getty Boris Johnson's cabinet: Who's in and who's out In: Dominic Raab Dominic Raab appointed foreign secretary AFP/Getty Boris Johnson's cabinet: Who's in and who's out In: Priti Patel Priti Patel appointed home secretary AFP/Getty Boris Johnson's cabinet: Who's in and who's out In: Michael Gove Michael Gove given Chandellor of the Duchy of Lancaster AFP Boris Johnson's cabinet: Who's in and who's out In: Sajid Javid Sajid Javid is appointed Chancellor of the Exchequer AP Boris Johnson's cabinet: Who's in and who's out Out: Jeremy Hunt Jeremy Hunt sacked as foreign secretary Reuters Boris Johnson's cabinet: Who's in and who's out In: Matt Hancock Matt Hancock remains health secretary AFP/Getty Boris Johnson's cabinet: Who's in and who's out Out: Chris Grayling Chris Grayling resigned as transport secretary Getty Boris Johnson's cabinet: Who's in and who's out Out: Jeremy Wright Jeremy Wright sacked as culture secretary PA Boris Johnson's cabinet: Who's in and who's out Out: Karen Bradley Karen Bradley sacked as Northern Ireland secretary Getty Boris Johnson's cabinet: Who's in and who's out Out: James Brokenshire James Brokenshire sacked as housing and communities secretary Reuters Boris Johnson's cabinet: Who's in and who's out Out: Penny Mordaunt Penny Mourdaunt sacked as defence secretary Reuters Boris Johnson's cabinet: Who's in and who's out Out: Liam Fox Liam Fox sacked as international trade secretary Getty Boris Johnson's cabinet: Who's in and who's out Out: Greg Clarke Greg Clarke sacked as business secretary PA Boris Johnson's cabinet: Who's in and who's out Out: David Mundell David Mundell sacked as Scottish secretary Getty Boris Johnson's cabinet: Who's in and who's out Out: Damien Hinds Damien Hinds sacked as education secretary Getty Boris Johnson's cabinet: Who's in and who's out Out: David Gauke David Gauke resigned as justice secretary EPA Boris Johnson's cabinet: Who's in and who's out Out: Rory Stewart Rory Stewart resigned as international development secretary Getty Boris Johnson's cabinet: Who's in and who's out Out: David Lidlington David Lidlington resigned as deputy Prime Minister PA Boris Johnson's cabinet: Who's in and who's out Out: Philip Hammond Philip Hammond resigned as Chancellor of the Exchequer AFP/Getty

Speaking as she celebrated her victory in the early hours of Friday morning, Ms Dodds called on Mr Johnson to rule out a no-deal Brexit.

The Welsh Lib Dem leader said: “People are desperately crying out for a different kind of politics. There is no time for tribalism when our country is faced with a Boris Johnson government and the threat of a no-deal Brexit.

“My very first act as your MP when I arrive in Westminster will be to find Mr Boris Johnson, wherever he is hiding, and tell him loud and clear: ‘Stop playing with the future of our communities and rule out a no-deal Brexit now’.”

Labour were pushed into fourth place by the Brexit Party, winning just 1,680 votes and a 5 per cent share, down 12 per cent on what they achieved in the constituency at the 2017 general election.

(Statista (Statista)

A Labour spokesperson said: “We always knew this was going to be a difficult night for us, but we’re proud of our positive campaign in Brecon and Radnorshire.

“One thing is clear – voters have rejected Boris Johnson and his divisive, out-of-touch Tory government.”

Mr Davies won the seat from the Lib Dems in 2015, as the party suffered disastrous results across the country that left it with just eight MPs, down from 57.

He was ousted by his constituents earlier this year after he pleaded guilty in March to submitting two false expenses invoices for nine photographs costing £700 to decorate his new office.

Mr Davies was fined £1,500, ordered to pay £2,500 towards legal costs and told to carry out 50 hours of community service.

The loss leaves Mr Johnson with the backing of 319 MPs in Commons, including the Democratic Unionist Party, while opposition parties now have 318.

And the national significance of the result showed in the turnout. At 59.7 per cent, it may have been down from 74.6 per cent at the general election, but it was the highest for a by-election since Winchester in 1997.

Lib Dem leader Jo Swinson said: “The people of Brecon and Radnorshire have shown that the country doesn’t have to settle for Boris Johnson or Jeremy Corbyn.

“Boris Johnson’s shrinking majority makes it clear that he has no mandate to crash us out of the EU.

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“As leader of the Liberal Democrats, I will do whatever it takes to stop Brexit and offer an alternative, positive vision for a richer, greener and safer future. Britain demands better than what the tired old parties can give.”

Plaid Cymru leader Adam Price hailed the “spirit of cooperation” between the pro-Remain parties as he called for a second referendum.