LONDON (AP) -- New British Prime Minister Boris Johnson was facing his first electoral test on Thursday -- a special election that could see the Conservative government's working majority in Parliament cut to just one vote.
Voters are electing a new lawmaker in a by-election for the seat of Brecon and Radnorshire in Wales after Conservative incumbent Chris Davies was ousted. He was dumped by a petition of local electors after being convicted and fined for expenses fraud.
Davies is running to regain the seat but faces a strong challenge from the Liberal Democrats' Jane Dodds in a vote overshadowed by Brexit.
In Britain's 2016 EU membership referendum the Brecon constituency -- a hilly, largely rural area about 175 miles (280 kilometers) west of London -- voted by 52%-48% to leave the EU, an outcome that exactly matched the national result.
As in the rest of the U.K., voters remain deeply divided over the decision, and over the fact that, three years later, Britain still has not left the EU.
Johnson became prime minister last week, vowing to take Britain out of the European Union on Oct. 31, with or without a divorce deal.
The pro-EU Liberal Democrats are hoping to win support from voters opposed to Brexit.
The centrist Lib Dems have just 12 of the 650 seats in the House of Commons but have seen their support surge because of their call for Britain to remain in the EU. In May's European Parliament election the party took 20% of U.K. votes, trouncing both the Conservatives and the main opposition Labour Party.
Johnson, who visited the area on Tuesday, said "a vote for any party other than Conservatives pushes the Liberal Democrats one step closer to cancelling the referendum result."
The Conservatives face a challenge for anti-EU voters from the Brexit Party led by longtime Euroskeptic figurehead Nigel Farage.
The Conservatives lack an overall majority in the House of Commons, and rely on an alliance with 10 lawmakers from Northern Ireland's Democratic Unionist Party.
If the Conservatives lose the Brecon seat, the governing alliance will have 320 of the 639 voting lawmakers --- the bare minimum needed to carry votes.
That will leave the government struggling to pass any legislation and vulnerable to an opposition no-confidence vote that could trigger an early general election.
Johnson has just over 90 days to secure and ratify a new divorce deal with the EU, or get Britain ready to leave the 28-nation bloc without one.
Economists say that would severely disrupt trade and plunge the U.K. into recession.