SCOTLAND would escape a new levy on its wealthiest citizens under plans for a mansion tax being considered by the UK Government.

In return for scrapping the 50p income tax rate on high earners, which Conservative critics suspect has failed to raise the £2.8 billion expected, Chancellor George Osborne, ahead of his March 21 Budget, is looking at a variation on the Liberal Democrats' desired mansion tax plan by introducing new super council tax bands to raise extra revenue from the better-off.

Nick Clegg, the Deputy Prime Minister, has argued it is unfair that someone with a house in the top band H – which kicks in at properties worth £212,000 in Scotland and £320,000 in England under the 1991 valuations – pays the same as someone whose home is worth several million pounds. New bands I and J for homes in excess of £1 million and £2 million could be introduced.

Yet council tax is devolved to Edinburgh, raising the possibility that the richest Scots, including oil barons and landed lairds, would avoid paying the Coalition's new wealth tax.

The move would undoubtedly spark political controversy among Conservative MPs in London and the southern English shires, who are already up in arms that any higher tax on property will hit their constituents the hardest.

Last night, a spokesman for the Scottish Government told The Herald: "The UK Government could not use the current council tax system to introduce a mansion tax in Scotland without the agreement of ministers and the Scottish Parliament. Any significant change would very likely require Scottish legislation."

Alex Salmond's Government believes council tax to be unfair, and has frozen it for the past five years and plans to do so until the next Holyrood election in 2016.

Stewart Hosie, the SNP's Treasury spokesman, said: "Should the UK Government introduce a mansion tax to remove the 50p rate, it might well lead to some unintended consequences."

Tory grandee Sir Malcolm Rifkind, who represents well-heeled Kensington and Chelsea, yesterday branded the proposed new wealth tax "arbitrary, unfair and unaffordable for many of those required to pay".

The former Conservative Scottish Secretary argued that if a new wealth tax were to be equitable it would "have to be based on a person's total wealth, not just their home".

He added: "If we are to target the super-rich for taxation, the least we can do is ensure that carelessness doesn't leave middle-income families caught in the crossfire."

Normal pre-Budget rules mean ministers do not talk about what might or might not be in the Chancellor's annual economic statement.

However, yesterday Vince Cable, the LibDem Business Secretary, made clear that Mr Osborne was considering a Coalition trade-off between scrapping the 50p tax rate in return for a new wealth tax on property.

He explained there was a "broad understanding" within the Coalition that if the 50p rate was scrapped, then it should be replaced by a new wealth tax, and his preferred property tax was an "economically sensible way of doing it".

Labour leader Ed Miliband said the mansion tax was "an idea the Government should look at but I don't think it should be used as an excuse to cut the 50p tax rate".

HM Revenue and Customs is looking at whether or not the new higher rate on incomes in excess of £150,000 brings in more money; it is due to report at the Budget.

Tory critics suspect it does not as the better-off find ways of avoiding it. They believe tax revenue is maximised at keeping the highest rate at 40p.

A combination of abolishing the 50p rate and introducing a new wealth tax on property that brings in more income and might fund a further raising of tax-free allowances could maintain the Coalition's political equilibrium and would be sold as a "fair package", whereby the rich help the poor – only not in Scotland.

Last night in a speech to the EEF manufacturers' dinner, the Chancellor said: "The days of unfunded giveaways are over and they're not coming back in this Budget. Everything has to be paid for."