Prime Minister Rishi Sunak has warned disillusioned Tory voters that a vote for Reform UK is "just a vote to put Keir Starmer in power," but who are they?

Last month, the rebranded Brexit Party won 13% of the votes in Wellingborough and 10.4% in Kingswood, its best-ever by-election results.

The numbers suggest most of Reform's support in Thursday's by-elections came from the Conservatives, who lost the seats with big swings to Labour.

Analysis by polling expert Prof Sir John Curtice shows that, for every voter who has switched since 2019 from Conservative to Labour, there is another one who has switched to Reform UK.

Who are Reform UK?

Reform UK was originally the Brexit Party. Throughout 2021 and 2022, the right-wing party fared poorly in the polls.

However, following the collapses of the Boris Johnson and Liz Truss administrations towards the end of 2022, things started to tick up.

Reform's standing in the polls began rising, as both the Conservatives and Liberal Democrats struggled against a surging Labour.

Mr Richard Tice, who was a Conservative Party member before Brexit, is the current leader of Reform UK. Tice has previously said he wants to "smash" and "destroy" the Tory Party at the general election.

He has insisted Reform UK would never consider repeating the Brexit Party's 2019 deal with the Conservatives - which saw it withdraw candidates in 317 constituencies after then-Tory leader Boris Johnson committed to leaving the EU by 2020.

Reform's pitch is to voters disaffected with both main parties - and Mr Tice has been equally scathing about Labour.

The four main policies are lower taxes, net zero immigration, cheaper energy, and zero waiting lists.

Other policies include keeping "woke ideologies out of the classroom" and abolishing the TV licence fee.

It also wants the UK to leave the European Convention on Human Rights, use offshore processing centres for illegal immigrants and prevent them from claiming asylum.

Speaking to Nicky Campbell on BBC Radio 5Live, Mr Tice said his party was "coming of age".

"More people are hearing about us and they're saying, actually, their policies, we like what we hear, we like that fresh approach, a very business-like approach," he said.

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What impact could Reform UK have on the next general election?

Speaking after the by-elections, former cabinet minister Sir Jacob Rees-Mogg said the Conservatives needed to focus on appealing to voters who had turned to Reform, adding that there was "a lot of common ground" between the two parties.

He insisted support for Mr Sunak's leadership was "solid" and "by-elections don't change that".

A right-wing Tory source told the BBC's Chris Mason: "The reality is Labour are currently storming to a huge victory and we have an insurgent party on the right polling above 10%.

"Cue Nigel Farage's intervention two months out from a general election and we're facing an extinction-level event. It's a slow-motion car crash."

"That's the actual choice at the general election, between me and him, between the Conservatives and Labour"

Mr Farage, who is popular among all UK right-wing voters, is currently honorary president of Reform. He is expected to campaign hard for the group, encouraging the disillusioned to switch allegiances.

The official Conservative line is that a vote for Reform is in effect a vote for Sir Keir Starmer's Labour Party.

Prime Minister Rishi Sunak said: "A vote for anyone who isn't the Conservative candidate, whether that's Reform or anyone else, is just a vote to put Keir Starmer in power.

"That's the actual choice at the general election, between me and him, between the Conservatives and Labour."