Tory whips are working hard to assess which MPs might be tempted to follow Douglas Carswell and Mark Reckless by defecting to Ukip if the party wins a second parliamentary seat in the Rochester and Strood byelection. Among those seen as possible defectors are:

• Philip Hollobone, the highly eurosceptic MP for Kettering, is seen as one of the most likely Tories to defect. Hollobone is a regular rebel who is one of four Tory MPs carrying out local polls on Britain’s EU membership in the same way as Reckless and Carswell did before their defections.

Hollobone, who has denied he is planning to defect to Ukip, is also a supporter of the anti-EU Better Off Out group. In a statement on its website he said: “Millions of British people have never had the chance to vote on whether or not to be in the EU. In 2006, you have to be at least 49 years of age to have taken part in the last UK referendum on Europe.”

• John Baron, another serial rebel who has been highly critical of David Cameron’s foreign interventions, is also high on the list of potential defectors.

The prime minister, who has been dismissive of Baron in the past, showed the Tory leadership was treading carefully with potential defectors when he made a point of lavishing praise on him in the Commons when the MP for Basildon and Billericay called on the government to pay £25m to nuclear test veterans. “I pay tribute to my honourable friend who has been dogged in pursuit of this very important cause,” Cameron said.

Baron declined to rule out joining Ukip last month. He told Newsnight: “You should never say never in politics but the bottom line is my very strong preference is to stay within the Conservative party.”

• Peter Bone, the Conservative MP for Wellingborough, prompted renewed suspicions that he might be planning to defect when he followed Reckless and Carswell in holding a local EU poll in his constituency. Bone, in common with other Tory MPs holding the polls, has been advised by Chris Bruni-Lowe who worked for Carswell before his defection, according to the Daily Mail.

Bone admitted his mini-referendum was a “crib” of the one used by Reckless. But he insisted that he was not about to defect. Asked by the Daily Mail whether he was considering a defection, he said: “I deny that 10,000%. I have been a member of the Conservative party since I was 15. I believe we should have a pact with Ukip [but] I have never had any discussions with anyone in Ukip about defecting.”

• Martin Vickers, the MP for Cleethorpes who is also holding a mini-EU referendum, admitted he had been approached by Ukip, who had offered not to challenge him in exchange for a free run in Grimsby.

Vickers told the Mail: “From a purely selfish point of view, that would be quite welcome, but I can’t deliver it. Even if the local party was willing to do it, we’re a national party and we will have a candidate in every seat.” But Vickers said there was “absolutely no way, under no circumstances whatsoever” that he would defect.

• Philip Davies, the MP for Shipley who is a member of the Better Off Out group, regularly confronts Cameron over Europe. But their humorous exchanges – and his friendship with the work and pensions minister Esther McVey – suggest Davies would think very carefully before defecting.

In his statement on the Better Off Out group, Davies wrote: “Our country built our prosperity as world traders. Our future prosperity depends on us trading with China, India, the rest of the Commonwealth and across the globe. It does not depend on being tied up in a backward-looking, inward-facing, protection racket designed to prop up inefficient continental farmers and businesses. We want free trade with the EU, but we do not need to be members of it to have that.”