Eurosceptic Tories are worried that Nigel Farage's perceived victory in his televised debate with Nick Clegg could cost the Conservatives dear at the 2015 general election.
A snap YouGov poll published minutes after Wednesday night's debate ended showed that some 57% thought that the Ukip leader performed best, compared to 36% for the Lib Dem leader.
While the debate was notionally a head-to-head fight between Farage and Clegg, the two men were in reality deliberately speaking to entirely different audiences.
For Farage, the debate was the perfect stage from which to convince eurosceptics that he, not David Cameron, that was the authentic anti-Brussels voice.
Bill Cash, the face of backbench Tory euroscepticism, said on Wednesday evening that Farage was "splitting" the anti-EU vote in such a way that it would let in a Labour government at the next general election.
"He was trying to take away the votes in our marginal seats when we are the only people who can deliver the policy because we will have enough members in the House of Commons to win the general election to make the changes," he said.
Cash, speaking to LBC radio, the hosts of the first debate, said Farage was was sucking up all the oxygen that should be shared with other anti-EU politicians. "I think that actually the amount of coverage he gets, on the BBC for example, is monumental. He's on the whole time. It's to split the eurosceptic vote."
He added: "The fact is we've [Tory MPs] done the work and actually he's getting all the airtime. He's getting a discorporate amount of attention given the fact he can't change anything."
Farage has bet everything on Ukip coming first in this May's European elections. But the real prize in the 2015 general election in which the party hopes to be able to secure its first Westminster MPs. Many Conservative backbenchers are worried that in crucial marginal seats the haemorrhaging of only a few centre-right votes to Ukip could let Labour candidates through the middle and see Cameron fall short of a majority.
Arch-eurosceptic Tory Peter Bone, who was patrolling the media spin room on Wednesday evening, indicated he felt Cameron's absence could have hurt the party. "It would have been good to be there to tell them we're the only ones who can offer an answer," he said.
Mid Bedfordshire Conservative MP Nadine Dorries said news coverage of the debate had been so anti-Farage and pro-Clegg that "the media are driving the public into UKIPs arms!". Tory defence minister Andrew Murrison said the clash was "an amusing diversion" but "the stark choice is PM Cameron or (aggh!) PM Miliband".
The Tory message that a vote for Ukip is a vote for a Labour government could damage Farage and he took it on directly during the debate. "The myth is that UKIP take Tory votes, therefore will damage the Tory Party and that will lead to a Miliband government," he said. "The truth of it is only one in three UKIP voters is a former Conservative. We pick up the bulk of our votes from old Labour and from non-voters getting back into politics."
Peterborough's anti-EU Tory Stewart Jackson had a more even handed view of who he wanted to win. "It's like Iran-Iraq war - I wanted both to lose," he tweeted. "However I find #cultofNige a bit creepy."
For Clegg, the debate was a chance to encourage broadly pro-EU voters to put aside any animosity they have towards the Lib Dems and lend the party their votes in the interests of holding back Ukip.
"Quitting Europe, would put all of that at risk. All of it. it would turn us into a country we don't want to be," he said. "I want us to be Great Britain, not little England. And if you feel the same, then now is the time to make your voice heard."
Clegg added: "If you believe that we are better off 'in', then at least on this occasion, in the European elections, I hope you will give us your support."
A Lib Dem source said the party was not even pretending to try and persuade the eurosceptic voters that form Farage's base of support: "We're not worried about them, they're not going to vote for us," the source said.