CHANCELLOR George Osborne appears poised to introduce an "oligarch tax", stinging wealthy foreigners who have forced up high-end property prices in the UK, and which will produce a new pre-election windfall for the Treasury.

Nick Clegg revealed yesterday that discussions were under way within the Lib-Con Coalition on introducing capital gains tax (CGT) on non-UK-based real estate owners.

While the Deputy Prime Minister stressed no decisions had yet been taken, one senior Coalition source later made clear that an announcement could come as early as Mr Osborne's autumn statement next month.

The Liberal Democrat insider stressed how the party still wanted to slap a 1% annual mansion tax on the value of properties over £2 million but the Conservatives were heavily against this. However, a move to hit foreign owners of very high-end property, sometimes left vacant for years, was being seriously considered.

Asked if the Lib Dems were pushing at a closed or open door on this, the source replied: "It's ajar."

The option being considered is imposing CGT of 28% on the sale of second homes in the UK that are owned by overseas investors. The new policy is designed to address concerns that a price bubble is being created by foreign buyers from countries such as Russia and Greece, who regard luxury flats and houses in the UK capital as a safe investment, producing healthy returns and often left empty after purchase.

"There are parts of the London property market now which are entirely divorced from and dislocated from the rest of the economy," explained Mr Clegg.

"That is party because they are driven by market forces which are global and by very, very large amounts of money flowing into the residential property market as an investment."

Stressing how Britain had to be an open economy, the DPM nonetheless argued that wealthy foreign investors had to "pay their fair share of tax on those transactions".

Mr Clegg insisted any changes in CGT should not be seen as a "surrogate" for the mansion tax.

He also indicated the Lib Dems would be ready to consider alternative methods of shifting the burden of tax away from earnings and on to wealth such as the introduction of new higher-rate bands of council tax to cover more expensive properties.

The signal on CGT came as the Free Enterprise Group of Conservative MPs put forward a £16 billion package of tax cuts, including scrapping stamp duty on house sales up to £500,000, raising the earnings threshold for higher-rate income tax to £50,000 a year and freezing business rates for three years.