Concerns are growing that the flourishing super-prime property market could be destabilised by threatened changes to non-domicile taxation rules that are just two months away.

Foreign-born property owners are in emergency talks with wealth managers and tax advisers to minimise the effect of the changes, outlined in draft legislation released a few weeks ago.

Mike Warburton, a tax partner at the accountant Grant Thornton, said: “The days of the offshore trust as a vehicle for avoiding tax on property are numbered - to 57 days, to be precise.”

Under the existing rules, non-domicile residents can enjoy tax-free capital gains on UK properties, if they are held by an overseas trust. But tax advisers warn that from April 6 such proceeds from trusts will be taxable.

Unexpectedly, the capital gains will be taxable even if a non-domicile resident has paid the £30,000 levy that the Government has promised will allow them to keep their offshore earnings tax-exempt.

Mr Warburton said: “Any well-advised non-domicile UK resident is rapidly getting their assets out of trust. It is an absolute shambles, but I fear the Government is going to press ahead because it is scared to change its mind.”

The Society of Trust and Estate Practitioners (Step), has cautioned it may lead to a “firesale of UK assets”. Jacob Rigg, parliamentary officer at Step, said: “People are looking to realise the gains on their assets over the next few months. They are potentially going to have to pay a whacking great amount of tax. The draft legislation is, for a lot of people, as bad as it gets.”

The most robust part of the market is super-prime homes - those valued at £4 million or more. Concerns about the future of the City, and lower bonuses have afflicted prime properties, priced from about £1 million. But this has been offset by demand for super-prime homes and Knight Frank reported that last month prime property prices in London rose 1.1 per cent — to an annual rate of 26.2 per cent.

Chesterton says 60 per cent of homes over £2 million in Central London are sold to foreign buyers, while Savills says 65 per cent of houses over £4 million are sold to foreign owners.

Robert Bartlett, chief executive of Chesterton, said: “The effects of the tax changes could be dramatic, destabilising London as a financial centre and hitting the housing market.”