Media playback is unsupported on your device Media caption BBC Wales reporter Teleri Glyn Jones talks to voters at the Royal Welsh Show

Voters go to the polls on Thursday to vote in the Brecon and Radnorshire by-election. It will be the first electoral test of the new prime minister, Boris Johnson.

But why does this particular election matter so much?

Why is it happening?

A by-election takes place outside a general election when a seat in the House of Commons becomes available.

In this case, the sitting MP Chris Davies was unseated after 19% of Brecon's voters signed a recall petition following his conviction for a false expenses claim.

Despite his conviction (for which he pleaded guilty), the Conservatives have reselected him as the party's candidate.

Alongside Mr Davies, candidates from five other parties (Labour, Lib Dem, Brexit Party, UKIP and Monster Raving Loony) will also be standing.

What is a recall petition?

The recall procedure is a relatively new innovation - it has only been available in the UK since 2015.

It allows the electorate the chance to trigger an election in special circumstances. These are:

An MP is convicted of an offence and sentenced to prison for less than a year (and has exhausted all appeal routes)

An MP is suspended from Parliament for more than 10 sitting days, following a report by the Committee on Standards

An MP is convicted of making false or misleading Parliamentary expenses claims

If an MP is sentenced to a year or more in prison they automatically lose their seat - so no petition is necessary.

Once a petition is open, voters registered in the area the MP represents have six weeks to sign it. For an MP to be unseated, at least 10% of eligible voters need to sign.

Image copyright Getty Images Image caption The by-election was triggered after 19% of voters signed the recall petition to remove Chris Davies

If an MP is removed, they are allowed to stand in the forthcoming election - something Mr Davies has chosen to do.

If the required number of signatures is not reached, the MP remains in post.

The Brecon by-election is only the second time an election has been triggered in this way.

The previous occasion was the Peterborough by-election, held on 6 June 2019. It was triggered after the sitting Labour MP, Fiona Onasanya, was convicted for lying about a speeding offence.

The only other MP subjected to a recall petition was the DUP's Ian Paisley in 2018. The petition was opened after Mr Paisley was suspended from the House of Commons for 30 sitting days. On that occasion, the petition did not attract enough signatures - so Mr Paisley kept his seat.

Why does the result matter?

Image copyright Getty Images Image caption Voters in Brecon and Radnorshire go to the polls on Thursday

Given the government's wafer-thin majority in the House of Commons, there is a lot at stake.

The Conservatives are defending a majority in the constituency of just over 8,000. Should they lose the seat, it will cut their working majority in Parliament to just one.

Such an outcome could make it harder for Boris Johnson to deliver Brexit on 31 October and would leave the prime minister more susceptible to losing a possible motion of no confidence.

The anti-Brexit Liberal Democrats will be seeking to capitalise. Their new leader, Jo Swinson, will be keen to make an immediate impact. Her party previously held Brecon, before it fell to the Conservatives in 2015.

The Lib Dems have been supported by two other anti-Brexit parties - Plaid Cymru and the Greens. Both have agreed not to stand this time, to give the Lib Dems a better chance of winning.

The candidates standing in the election are: Chris Davies, Conservative Party; Tom Davies, Labour Party; Jane Dodds, Liberal Democrats; Des Parkinson, Brexit Party; Liz Phillips, UKIP; Lady Lily The Pink, Monster Raving Loony Party.

You can find more about each one here.