Polls have closed in the Brecon and Radnorshire by-election in the first major challenge for Boris Johnson as Prime Minister.
The new Tory leader could be dealt a significant blow if the Conservatives do not win, with his working majority falling to just one.
The Liberal Democrats, who held the seat until 2015, are seen as the major threat but officials from both parties believe the outcome will be close.
A Tory loss could make Mr Johnson’s challenge to steer Brexit through Parliament even harder and increase the chances of a snap general election.
The by-election was triggered when Tory MP Chris Davies was ousted in a recall petition after he admitted submitting false invoices for expenses.
Some 19% of the electorate voted for his recall, well above the 10% threshold required.
Despite this, the Conservatives selected Mr Davies to try to win the seat back.
His main challenger is the Lib Dem’s leader in Wales, Jane Dodds.
The vote is also a test for the fledgling “Remain alliance” of anti-Brexit parties, with Plaid Cymru and the Greens agreeing not to field candidates in order not to split the pro-EU vote.
Commons Leader Jacob Rees-Mogg and Chancellor of the Duchy of Lancaster Michael Gove have both visited the constituency in recent weeks.
So too has Mr Johnson, though his presence was interpreted as having been muted.
The loss would be significant for the PM, leaving him with the support of 319 MPs, including the DUP which props up his majority.
The opposition would have 318.
Mr Davies secured a majority of 8,038 at the 2017 general election.
The Tories took 49% of the vote, Lib Dems 29%, Labour 18%, Plaid Cymru 3% and Ukip 1%.
The Lib Dems, who held the constituency from 1997 until Mr Davies’s first victory in 2015, would need a swing of 9.8% to retake the seat.
Mr Davies’s recall came after he pleaded guilty in March to submitting two false expenses invoices for nine photographs costing £700 to decorate his new office.
He was fined £1,500, ordered to pay £2,500 towards legal costs and told to carry out 50 hours of community service.
The result of the by-election is expected at around 3am on Friday
The other candidates are Labour’s Tom Davies, the Brexit Party’s Des Parkinson, Ukip’s Liz Phillips and the Loony Party’s Lady Lily The Pink.