More UKIP defectors? Tory MPs linked to rival party
Tory MP Douglas Carswell's surprise defection to UKIP has prompted speculation about whether other Eurosceptic Conservatives may also be considering jumping ship.
UKIP leader Nigel Farage has said he is "constantly" talking to like-minded Conservatives - and Labour MPs - while the party's Treasurer Stuart Wheeler says he has had discussions with eight Tory backbenchers. He has declined to name names - but that has not stopped speculation about who might be next.
Especially after Mr Wheeler told BBC Radio 4's The World at One it was "odds on" that other MPs would follow Mr Carswell.
Here are some of those who have been linked to UKIP in the past - and what they have said in response to Mr Carswell's defection.
Philip Hollobone (Kettering - majority 9,094)
Background: First elected in 2005, Mr Hollobone supports the UK's exit from the European Union and has constantly rebelled against his party over Europe. He has been a thorn in the side of the coalition, backing an alternative Queen's Speech in 2013 and calling for restrictions of the wearing of the burqa in public.
What UKIP says about him: UKIP did not put up a candidate against him at the 2010 election arguing that - like Mr Carswell - he was a committed opponent of the EU.
What he says about UKIP: Last year, Mr Hollobone said he could have lost his seat without UKIP's endorsement and has called for an electoral pact between the parties in 2015 to ensure UKIP does not stand against Conservatives who want to leave the EU.
Prospects: He has not commented yet on Mr Carswell's defection but is among those Tories most sympathetic towards UKIP. However, Northamptonshire is not seen as natural UKIP territory.
Nadine Dorries (Mid-Bedfordshire - majority 15,152)
Background: One of the most outspoken women in the Conservative Party, the former nurse was briefly suspended in 2012 after appearing on ITV reality TV show I'm a Celebrity. A strong supporter of change in Europe, she has called for a referendum to be held as soon as possible.
What UKIP says about her: In 2012, deputy UKIP leader Paul Nuttall said the Tories were worried about Ms Dorries defecting but admitted he had never spoken to the Conservative MP.
What she says about UKIP: In 2013, she called for candidates to be able to stand on a joint Conservative-UKIP ticket if there was local support for the idea.
Prospects: Despite being a vehement critic of David Cameron, Ms Dorries has insisted she will not be joining UKIP, saying "only one party which can deliver on its promise is offering a referendum and that's the Conservative Party".
John Baron (Basildon and Billericay - majority 12,398)
Background: Former soldier who has been a frequent rebel on Europe, Mr Baron has also defied the party line on Libya and helped trigger the parliamentary rebellion against David Cameron on intervention in Syria. He has also accused No 10 of "complacency" over immigration.
What UKIP says about him: UKIP agreed with Mr Baron's stance on Syria but the party has been targeting his parliamentary seat as well as others in Essex.
What he says about UKIP: He has accused the Conservative leadership of "ignoring and then insulting" UKIP but has insisted there should not be any electoral pact with Nigel Farage's party.
Prospects: Not David Cameron's greatest fan but has insisted he is staying put and ruled out co-operation with UKIP. UKIP has been gaining strength in Basildon, winning 11 seats in May but Mr Baron has a 12,000 majority to defend in his Conservative stronghold.
Peter Bone (Wellingborough - majority 11,787)
Background: Like his Eurosceptic colleagues, a frequent rebel on Europe but has also called for the coalition to be broken up and for the Conservatives to rule as a minority government.
What UKIP says about him: UKIP says candidates such as Mr Bone could have the endorsement of two parties with two logos on their ballot paper.
What he says about UKIP: Has called for a "holy alliance" with UKIP to harness Eurosceptic forces at the next election. But he has described Douglas Carswell's defection as "very disappointing" and suggested a strong UKIP vote in 2015 will let Labour into office.
Prospects: Has said he understands why people vote UKIP but has described his colleague's defection as a mistake and said that he, personally, is a "Conservative through and through".
Jackie Doyle-Price (Thurrock - majority 92)
Background: Has one of the slimmest majorities in the country after being elected to Parliament in 2010. Constituency is very eurosceptic but she has backed David Cameron on Europe, saying all Tory MPs should be able to support his "strong" position on a referendum.
What UKIP says about her: Thurrock has long been one of UKIP's target constituencies. The party has lined up one of its heavyweights, policy director Tim Aker, to contest the seat, suggesting they are not expecting her to join them.
What she says about UKIP: Much more critical than many of her colleagues. Criticised Nigel Farage's comments on Romanian immigrants during this year's European election campaign, saying they could "inflame racism".
Prospects: Has called on Tory MPs who support UKIP to join them, insisting she is not one of them.
Jacob Rees-Mogg (North East Somerset - majority 4,914)
Background: An old-school Conservative, the old Etonian has joined rebellions against the government over Europe and House of Lords reform. He was the first Tory MP to call for his party to co-operate with UKIP at a local level in 2015.
What UKIP says about him: At a fringe event at the 2013 Conservative conference, Nigel Farage suggested it was in the "national interest" to have MPs like Mr Rees-Mogg in Parliament and UKIP may not challenge him at the election.
What he says about UKIP: In 2012, he floated the idea of an electoral pact with UKIP but has said speculation about him joining UKIP is "silly".
Prospects: Ruling out such a move to UKIP, he said he believed Mr Carswell had made a mistake and his resignation would not make much difference. "Individuals switching parties get remembered by political anoraks, when 20 do and set up a new party, that is when it is important," he told the BBC.
Philip Davies (Shipley - majority 9,944)
Background: The keen horse-racing enthusiast and Thatcherite MP is a scourge of the Europhile wing of the Conservative Party.
What UKIP says about him: Mr Davies, one of the Better Off Out group of Tory MPs, which campaigns for Britain's exit from the EU, was not challenged by UKIP at the 2010 general election. Nigel Farage has suggested UKIP could make "common cause" with him again in 2015.
What he says about UKIP: Mr Davies has praised Mr Farage in the past, saying he "wiped the floor" in his debates with Nick Clegg before May's European elections. But he also believes backing UKIP could usher in a Labour government which would oppose a referendum.
Prospects: Told the Financial Times that Mr Carswell's exit was "misguided" and suggested his former colleague was more of an "anarchist than a true Conservative".
Mark Pritchard (The Wrekin - majority 9,450)
Background: The MP quit his role as deputy chairman of the party in 2012, citing differences with the leadership over Europe, immigration and efforts to promote social mobility.
What UKIP says about him: In a blog post last year, the UKIP association in Mr Pritchard's constituency said the MP had some "decent qualities" but he would have to work "very hard" to convince the party of his sincerity should he seek to join them.
What he says about UKIP: He has claimed a vote for UKIP in 2015 is tantamount to a vote for Labour, arguing the Conservatives are only party that can deliver a referendum.
Prospects: He has predicted that no other Conservative MP will join UKIP before the election, irrespective of the outcome of the Clacton by-election.