David Cameron was last night warned by his own candidates that he has to sharpen his attacks on Nick Clegg in next week's televised leaders' debate to counter a "yellow surge" after being eclipsed by the Liberal Democrat leader in the first round.
Mr Cameron appeared to pull his punches and now faces a dilemma over whether to mount more aggressive attacks as he reviews his strategy with key advisers this weekend.
Senior Tories denied there were jitters over Mr Cameron's performance, and were delighted that their own research showed he had done well on health and education. However, some were privately disappointed that his showing was not strong enough to prevent Mr Clegg from stealing the limelight. "It was supposed to be about us, not him," said one Tory candidate.
The inquest among some Tories focused on the three-party format. "We should never have allowed Clegg to have an equal footing. That was a big mistake," said one party insider.
Tory officials said that lessons would be learned – a sign that Mr Cameron might become more aggressive in the next two debates. They said there was a delicate balancing act to be struck between "being prime ministerial and landing blows in a way that is not very statesmanlike".
Speaking to reporters on his battlebus as he toured key marginal seats in the North West, north Wales and Wolverhampton, the Tory leader publicly insisted he would not change tactics or "go negative" in the debates. "I do not believe in being negative and trying to pull the others down," he said.
Praising Mr Clegg's performance, he added: "There is no doubt that a 'plague on both your houses' is a good song to sing and he sang it very effectively."
He said that Gordon Brown had been "very negative", did not "have much to say" and had not got "off the ground". It had been "hysterical", he said, that Mr Brown had made continued overtures to Mr Clegg, "but Nick wasn't having any of it".
A "Lib Dem yellow surge" in the south and west on the back of Mr Clegg's success could destroy Tory hopes of gaining 23 Lib Dem seats crucial to their chances of winning an overall majority. Conservative supporters in Prestatyn urged Mr Cameron to step up attacks on Mr Clegg, particularly on his pro-Europe stance, to counter the Liberal Democrat threat.
Mr Cameron said voters needed to recognise that Mr Clegg had no prospect of taking power. One former Tory minister campaigning in the south said: "He does need to be sharper and I'm sure he will be in the next round. The big one is the economic debate in a fortnight. He has to win that."
Mr Cameron managed to avoid being eclipsed – just – for a second time in 24 hours when he shared a platform with Take That star Gary Barlow in front of an audience of excited comprehensive schoolchildren. Asked whether he backed Mr Cameron after joining the Tory leader in launching a new plan for a national "School Stars" competition for budding musicians, Mr Barlow said: "I wouldn't be here if I wasn't.''
Mr Cameron admitted later that he had been nervous ahead of Thursday's debate, adding: "We were all a bit nervous. But I was happy with it. I got across the answers I wanted to."
Former Cabinet minister Lord Tebbit said it was no wonder Mr Cameron "looked a little disgruntled" after the debate because Mr Clegg promised the earth "and got away with it..."
Lord Tebbit said Mr Cameron "scored points" on immigration, but the Tory leader is expected to resist the temptation to raise immigration higher up the agenda to avoid a charge of using the race card, which proved counter-productive for his predecessor, Michael Howard, in the 2005 election.
Mr Cameron went to the marginal constituency of Wolverhampton South West for a Q&A session with the staff at Asda. The Midlands is a key target area for the Tories – they lost this seat by just five per cent in 2005. But local voters had mixed views on both his politics and his performance. Taxi driver Steven Kumar, 32, said he was thinking of switching from Labour to Conservative after seeing him on TV.
"He does know how to talk to people," he said. "He can relate to people much better than Gordon Brown can. As long as he doesn't turn into Mrs Thatcher then he might be all right!''
But Joan Smith, 83, said: "I watched the start of the debate but I turned it off once they started arguing. You can get all of that from soap operas; I thought it was pathetic how much they bickered with each other. I don't trust David Cameron at all... I think they're having that baby for publicity."
The Conservative leader will address a rally today after returning to London.
One down, two to go: In the blue corner
*Strengths to play to
Young family man with the energy and ideas to do the job. Not frightened to take the tough decisions necessary to rebuild the economy. The only person who can stop five more years of Gordon Brown; voting Liberal Democrat will let Labour back in.
*Weaknesses to correct
Has to be more aggressive and land more punches on his rivals. Betrayed signs of nerves and never showed much passion. For a good television performer, was surprisingly wooden.
Coming across as a slick salesman without true convictions. Allowing his privileged background to alienate wavering voters who think he has little in common with them.