Nick Clegg has appeared to row back from a proposal for a tycoon tax built round a minimum tax rate.

Clegg had said he was attracted by Barack Obama's idea of a tycoon tax in which the rich are required to pay a proportion of their income in tax. President Obama has made the Buffett rule – mandating that millionaires pay at least 30% of their incomes in taxes – the centrepiece of his campaign for "fairness", including in his state of the union address last month.

But in a speech to the Liberal Democrat spring conference on Sunday, Clegg made no reference to a minimum tax for the rich, saying more broadly: "We will call time on the tycoon tax dodgers and make sure everyone pays a fair level of tax."

Lord Oakeshott, the wealthy Liberal Democrat peer and close ally of the business secretary, Vince Cable, had described Clegg's proposal as "a superficially attractive measure that falls apart under scrutiny and does nothing to do with the super rich non-doms and non-residents".

Clegg took a swipe at Oakeshott in his speech, claiming "the only person who argues against a tycoon tax is one of our very own tycoons". The infighting reflects tensions over the viability of the proposal and the way in which it was sprung on colleagues.

Cable and his ally Lord Newby have been pressing for a mansion tax, as well as measures to hit pension tax relief in the upcoming budget, regarding them as better ways of raising the cash needed to fund an increase in personal tax allowance. Newby, who led a party tax commission, was dubious that a tycoon tax would not just see millionaires redefining income as capital.

Clegg's aides had briefed that Oakeshott was isolated and predicted that Cable would issue a statement in support of the plan. Instead, he said: "I have not seen the details of the proposals so I cannot give you a very informed comment. The idea is an interesting one."

Danny Alexander, the treasury chief secretary, was more enthusiastic, saying a tycoon tax "is one of a number of ideas that we have as a party. I think it's a very interesting and good idea. It's one that could really help to ensure the thing that we all need to do as a country, which is to make sure that the wealthiest of this country pay their fair share of tax."

The row obliterated some of the broader tax messages in Clegg's speech. He promised: "We will call time on the tycoon tax dodgers and make sure everyone pays a fair level of tax. Too often, rather than paying their dues the wealthy pay their accountants to get them out of it. Avoiding tax, minimising the amount they have to contribute – that's the name of their game. Boasting about the latest wheeze for moving an asset here, a property there and a loophole everywhere. All to make the tax bill lower."

He added: "Few things make me angrier as the unemployed struggle to find work, as ordinary families struggle to make ends meet, as young people struggle to get on the housing ladder: the sight of the wealthiest scheming to keep their tax bill down to the bare minimum is frankly disgraceful. Multimillionaires avoiding tax by moving their money around."

He hinted that he was opposed to seeing the top 50p rate for those earning more than £150,000 abolished in the budget, saying: "The last big tax-cutting budget was in 1988. Nigel Lawson cut billions from the tax bills of the highest-paid workers: a budget for the few, not for the many.

"But this year's coalition budget must be a budget for fairness – not an 80s Lawson budget but a modern liberal budget."

He also directed his fire at the chancellor, George Osborne, for suggesting in his conference speech that there was a choice between being green and backing growth. Clegg said: "What a load of rubbish. Going for growth means going green. The race is on to lead the world in clean energy. The new economic powerhouses – China, India, Brazil – are competing.

"So the choice for the UK is simple: wake up, or end up playing catch up. Going green is not a luxury for the good times. It is the best road out of the bad times.

"Our party is the green party of government. We have always been a green party. And let me tell you this: we always will be a green party because we need an economy fit for the future to pull us out of this economic downturn."