A series of anxious shadow ministers have warned the Tory leadership in private that David Cameron's central general election message – devolving power to create a "big society" – is crashing on the doorstep as candidates struggle to explain the idea to voters.

As Cameron's circle intensify their preparations for Thursday's television debate, by issuing pleas at Tory HQ for fresh ideas, shadow ministers have told the leadership that their "big idea" is too vague and needs to be scrapped in favour of practical policies.

The nervous discussions come as party officials experience a rollercoaster ride in the face of conflicting opinion polls. A ComRes poll for ITV/the Independent gave the Tories, on 35%, a nine-point lead over Labour and the Liberal Democrats on 26%. Other polls indicated that Nick Clegg was still on a roll after his success in last week's television debate.

The ComRes poll went some way to soothing frayed nerves among Tories who believe that the apparent Lib Dem surge has highlighted deep flaws in the Conservative campaign. Criticism is focusing on Steve Hilton, the director of strategy, and Oliver Letwin, the shadow cabinet policy co-ordinator, who were the main brains behind last week's Tory manifesto. This was entitled Invitation to Join the Government of Britain and was designed to illustrate the "big society" idea of handing power to people to set up schools and sack police chiefs.

But shadow ministers say the Letwin and Hilton approach is difficult to sell on the doorstep. "Oliver Letwin had this great 'big society' idea, though it might have been an idea to share it with the rest of us," one normally loyal shadow minister said. "People don't really follow Oliver's philosophical discourse."

Another shadow minister echoed this criticism. "The 'big society' needs to be turned into more practical, voter-friendly language. We need to turn Oliver Letwin's Hegelian dialectic into voter friendly stuff."

A third Tory source was even blunter. "The 'big society' is bollocks. It is boiled vegetables that have been cooked for three minutes too long. It tastes of nothing. What is it?"

Tories are agreed that it would be wrong for Cameron to embark on the sort of lurch to the right that destroyed William Hague's leadership. They say that the 'big society' strategy is right but needs to be illustrated with specific policy proposals.

The leadership appeared to respond to these criticisms today by unveiling a hardline poster featuring the party's policies to crack down on benefit cheats.

"Let's cut benefits for those who refuse to work," the poster says next to a picture of Cameron. Tim Montgomerie, the founder of the ConservativeHome wesbite, wrote tonight: "It's good to see the party getting specific about what 'change' means."

The new Tory poster

Cameron himself embarked on a slight change of tactics todaywhen he began a walkabout in the marginal seat of Tamworth, where he said he wanted to answer "the questions real people want to ask".

He took questions about free care for the elderly, immigration, the impact of fuel prices on hauliers and the future of the NHS.

The Tory leader, who will tomorrow visit the Lib Dem stronghold of the south west, gave his strongest warning of the danger of voting for Clegg. A hung parliament would "lead to a sort of stagnation to a sort of haggling and a bickering among politicians and we won't get done what so badly needs to be done in our country".

His tough language will please internal critics who are annoyed that the leadership is not selling flagship policies.

"We have some great policies but we're not talking about them," said one Tory. "I had no idea that we have a great idea to give 1 million more people access to an NHS dentist. What a great idea. Why aren't we shouting about that? … It is a great policy and nobody knows about it."

The criticism of the election campaign came amid the first signs of whisperings about Cameron's leadership. There was disbelief among some Tories when the leader responded to Clegg's strong performance by decreeing last Friday that nothing needed to change.

The leadership embarked on a rethink at the weekend, resulting in a hastily filmed personal statement by Cameron for an election broadcast on Monday night, when the Lib Dems surged in the polls.

One senior figure said: "The project is all about Dave. So if he succeeds it is about him. But if he fails it is about him."

The source was clear about what would happen if Labour and the Lib Dems formed a coalition in a hung parliament to push through electoral reform. "By then we would have murdered our leader and his head would be on a stake. The last week shows how thin our support was. There is no great enthusiasm for Cameron."