A Conservative MP has lost his seat after an expenses scandal, triggering a byelection that will provide a tricky test for the next prime minister.

A recall petition was set up after Chris Davies, the MP for Brecon and Radnorshire, was convicted of submitting fake expenses documents. He was ousted from the House of Commons after 19% of registered voters in his constituency signed a petition to remove him.

A total of 10,005 people signed, well above the 10% threshold needed for a recall. The result, confirmed on Friday by the Commons Speaker, John Bercow, means a byelection will be called, which Davies could stand in.

The seat was held by the Liberal Democrats from 1997 until 2015, when Davies won it. He increased his majority in 2017.

The Lib Dems have high hopes of winning the seat, which was visited by the party leader, Vince Cable, during the European elections. If the Conservatives lose, the new prime minister’s working majority in the Commons will be reduced to three .

At the leadership vote count on Thursday morning, two anonymous MPs spoiled their ballot papers in protest at the choice of candidates, raising questions about whether the next prime minister will be able to command the confidence of the Commons.

In recalls, the party in control of the seat – in this case the Conservatives – is in charge of moving the writ to determine the timetable of the byelection. If it is issued on Tuesday, that is likely lead to a byelection on Thursday 25 July, the day parliament breaks up for the summer recess, though it could be later if the Tories want to avoid a clash with a leadership election.

The timing means the byelection could be held after a new prime minister has been installed.

Q&A What is a recall petition? Show Hide Introduced as a result of the MPs' expenses scandal, the 2015 Recall of MPs Act governs a process by which an MP can lose their seat in the House of Commons if there is a successful petition to recall them. A petition is triggered if an MP is: Convicted of an offence and receives a custodial sentence (including a suspended sentence).

Barred from the Commons for 10 sitting days or 14 calendar days.

Convicted of providing false or misleading information for allowance claims under the Parliamentary Standards Act 2009. The petition is open for six weeks. If it is signed by at least 10% of people registered to vote in the constituency, the MP loses their seat and a byelection is held. There is nothing to stop the recalled MP standing again. People are allowed to campaign in the constituency to get the petition signed but, as with elections and referendums, there is a limit to how much they are allowed to spend. The first MP removed from office after a recall petition was Fiona Onasanya in May 2019, after she was found guilty of lying to avoid a speeding ticket. The second was Chris Davies, following his conviction for submitting fake expenses claims.

Jane Dodds, the Welsh Lib Dems’ parliamentary candidate for the constituency, said: “Thousands of residents across Brecon and Radnorshire have taken the chance to demand better than a Westminster politics that fails to take their concerns seriously.

“Now we have a golden opportunity to do things differently. The clear choice in this byelection is between the Conservatives, whose chaos and infighting is letting our communities down, and a better future for our area with the Welsh Lib Dems.”

Welsh Labour called on the Conservatives to immediately move the writ in parliament for a byelection. A spokesperson said: “The recall result is another huge blow to Chris Davies’ credibility to serve as member of parliament. This is a mess all of his making.

“Nine years of Tory austerity – enabled by the Lib Dems in the coalition government – have pushed communities to breaking point. The people of Brecon and Radnorshire deserve a Labour MP who will work every day to make a real difference in their lives. And Wales needs a Labour government in Westminster that will end austerity, invest in our public services and stand up for our people.”

A Plaid Cymru spokesperson said: “Ensuring those of us who want to see a fresh referendum work together, at every possible level, to deliver this aim is crucial. We will explore options for how we can work together, across party lines, to deliver this in the upcoming Brecon and Radnorshire byelection.”

Davies’ conviction was for submitting fake expenses invoices for nine framed landscape photographs, costing £700, to decorate his office in Builth Wells. He was fined £1,500 and ordered to complete 50 hours of community service.

During the sentencing in April, the judge Mr Justice Edis told Davies: “It seems shocking that when confronted with a simple accounting problem you thought to forge documents. That is an extraordinary thing for a man with your position and your background to do.”

Davies declined to speak to the Guardian this week before the petition closed. In a statement on his website, he said what he had done was an “administrative error” and he had not tried to make any financial gain. “I made a technical breach of a complicated accounts process and fell foul of a new law which is unique to members of parliament,” he said.

He has invited constituents into his office to view the documentation and the photographs.