Mr Mittal's spokeswoman said it was "private ... there is nothing illegal". Mr Ondaatje contacted the Labour party press office and then declined to comment. Mr Kaye's spokeswoman said his home was owned by a company "which is owned by a family trust". Mr David's secretary said: "It is private." Neither Mr Tabatznik nor his accountants had anything to say.

The ability to escape ordinary people's property taxes is not confined to Labour supporters.

Lady Thatcher registers ownership of her �3m London house not in the Thatchers' own name, but in the name of an anonymous offshore company.

Her Chester Square home acquired in 1991 is listed as owned by Bakeland Property Ltd on a 64-year lease. We have established that this is a Jersey company.

Its shares are held by two Jersey individuals who are the Thatcher family's financial advisers, Leonard Day and Hugh Thurston. They are acting as nominees for a trust with concealed beneficiaries, accountants say.

The former prime minister's office refuses to explain why she does not apparently own her own house. Leonard Day in Jersey said: "No one's going to tell you about that."

Other Conservative supporters using offshore ownerships include the former Tory MP for Torbay, Rupert Allason.

Recently described by a judge as "one of the most dishonest witnesses" he had ever seen, over his financial affairs, Mr Allason's �1m second home at Aldworth is in a picturesque English village on the edge of the Berkshire downs. It avoids tax, having been owned for the last 22 years by a Panama company, Polarpark Enterprises.

It has now emerged that the company is in turn owned by a trust whose beneficiaries in Bermuda are Mr Allason's children. (His wife was Bermudian and her foreign domicile appears to make this scheme legal). Mr Allason says: "Don't associate me with setting this up for tax purposes just because my ex-wife happens to be Bermudian. I don't know anything about the tax position."

A previous donor to the Conservative party is Wafic Said, a former operator of a kebab restaurant who made millions in commissions on a 1985 British Aerospace arms deal to sell Tornado fighters to the Saudi royal family. He has a �9m apartment in Eaton Square, one of London's most expensive addresses. But builders' cranes also tower over the Cotswolds countryside where he is erecting a Palladian mansion on the site of Tusmore House, a 3,000-acre estate he bought in 1987.

It is not registered as owned by him but by Tusmore Estates SA, an offshore company. Mr Said, too, claims non-domicile status to avoid paying tax on assets held abroad. His spokesman said: "It has been placed in a trust to make the arrangements simple for the family."

Mr Said's chief Saudi patron, Prince Bandar, has an even more palatial Cotswolds mansion a few miles away, together with a large farming estate and the entire village of Glympton. He is an absentee landlord, with the ownership registered offshore, in the name of a Jersey company listed in turn as owned by a bank official and an accountant.

Prince Bandar's estate manager explained that behind this lay a common scheme - a discretionary trust whose beneficiaries were members of the prince's family. He had been advised this would enable them to keep the property after his death. "Since he is not resident in this country, no liability

for tax arises under this structure."

One of the former Conservative government's more lavish supporters was Mohamed Al Fayed. As well as donating �250,000 in the 1980s, he also famously gave Tory MPs Tim Smith and Neil Hamilton cash in brown envelopes.

But his Surrey mansion, Barrow Green Court, and his Scottish castle at Balnagown, are not owned by him. They are registered to Bocardo, a company in the tax haven of Liechtenstein whose shares are believed to be held in turn at Banque Gonet in Switzerland and controlled by Mr Fayed and his two brothers.