A defeat for the Tories in this week’s by-election in the Welsh seat of Brecon and Radnorshire would shrink their working majority in the House of Commons to just one.
There are currently 320 MPs who – on paper – would back the government in a crunch vote in the House of Commons – 310 Tories and 10 members of the DUP.
The DUP agreed to support the Conservatives in certain key votes, such as confidence motions and Budgets, as part of a deal reached in the aftermath of the 2017 general election.
But with theLiberal Democrats favourites to win the seat, the opposition tally would increase from 318 to 319.
With the Tories and DUP unchanged on a combined total of 320, this would reduce the government’s majority from two to one.
The totals do not include Sinn Fein’s seven MPs, who do not take their seats in the Commons, and the speaker and three deputy speakers, who do not vote.
The Liberal Democrats need a swing of 9.8% to take the Welsh seat from the Conservatives.
MORE – Brexit Party bus is spotted stuck in a ditch and the jokes almost wrote themselves
MORE – ALASTAIR CAMPBELL: Why I no longer want to be readmitted to Labour
If they succeed it would put the party in a strong position at a general election, which could see the party pick up around a dozen seats from the Tories.
The Lib Dems held the seat of Brecon & Radnorshire from 1997 to 2015, since when it has been held by the Tories.
At the 2017 general election, the Conservatives’ majority was 8,038.
As part of a Remain alliance, Plaid Cymru and the Green Party are not fighting the by-election to give anti-Brexit party the Lib Dems a fair chance.
The six candidates standing in the by-election are:
Chris Davies (Conservative)
Tom Davies (Labour)
Jane Dodds (Liberal Democrats)
Des Parkinson (Brexit)
Liz Phillips (UKIP)
Lady Lily The Pink (Loony)
The by-election takes place on Thursday with the result expected early on Friday morning.