Nick Clegg lambasted David Cameron as infantile and juvenile and said that the time was coming when the Tory leader would face tough questions about his party's policies.

Mr Clegg used his debut on stage at the Liberal Democrats' annual conference to attack Mr Cameron's “ill thought-out, juvenile approach” to tax cuts that benefited the wealthy and only trickled down to those less well-off. “I don't think ordinary people deserve to be trickled on,” Mr Clegg told the audience in Bournemouth. It was the first time that Mr Clegg, 41, had addressed delegates as leader of the Liberal Democratic Party, having been elected at the end of last year.

Rather than use the platform to attack the embattled Gordon Brown, Mr Clegg seemed more intent on doing damage to his Tory counterpart. Defending accusations that he was “Cameron Lite”, Mr Clegg criticised what he called Mr Cameron's “infantile reaction” to last month's conflict between Russia and Georgia. The Tory leader, he said, “flew off to Tbilisi for a photo-shoot”, adding that it was classic Cameron hypocrisy to demand that Europe present a united front against Russia while at the same time proposing the break-up of the EU.

Mr Clegg gave warning that the British public would soon start asking Mr Cameron some difficult questions. “I think they are doing the easy bit now, which is muddying the water, saying they are everything to everyone.

“The hard bit is when people will ask him in the next few months: what will you actually do? Are you prepared to make those tough choices?”

Mr Clegg's attacks on Mr Cameron's tax policies come as he faces a potential revolt today about his plans to rebrand the Liberal Democrats as tax-cutters. He has pledged to identify £20 billion in savings across Whitehall. The money would be allocated to the Liberal Democrats' own spending priorities and any left-over cash would be used to fund additional tax cuts, on top of a 4p reduction already promised in the basic tax rate.

He faces a clash with rebel MPs on the left of the party who believe that tax cuts have been placed too high up the agenda at the expense of other priorities such as tackling poverty and improving health services and education.

Evan Harris, the party's science spokesman, said that the public had been given mixed signals about the tax cuts, with some people believing all £20 billion would be spent on reducing the tax burden for low and middle-income voters. Dr Harris has tabled an amendment insisting that further cuts should be considered only as a secondary policy.

Mr Clegg urged delegates to back his plans and “go one step farther” on tax. He said that he wanted to help those who had been really struggling and paying out more of their income in tax than the wealthy.

Vince Cable, the party's economic spokesman, will continue to make a case for tax cuts in a speech today, when he will also outline a six-point plan to generate £5 billion from closing tax loopholes on business and the rich. Mr Cable will say: “The Liberal Democrats are committed to ensuring that families on low and middle incomes pay less tax. However, we must ensure that those at the top are paying their fair share.”

Mr Cable will say that between £10 billion and £40 billion a year in tax is being avoided. Among the proposals are plans to prevent sacked businessmen - such as Adam Applegarth, the former chief executive of Northern Rock - from walking away with tax-free windfalls. Businesses will also be made to pay their fair share of stamp duty when buying property and so called “non-dom” foreign workers will also be made to pay more taxes.

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