Squatters have moved into a London super-mansion in a road dubbed “Billionaires’ Row”, a few doors from a house owned by the steel magnate Lakshmi Mittal.

Mr Mittal, the head of ArcelorMittal, put his home, the nine-bedroom Summer Palace, on the market last year at £40 million before deciding not to sell it, according to local estate agents.

The squatted-in house is in The Bishops Avenue, in North London, a favoured address among international businessmen and heads of state, where it is not uncommon for mansions to have heated driveways, security guards and their own beauty parlours. However, this property, like many others in some of London’s most prestigious streets, was left empty and run-down years ago, according to its new occupants. High-profile neighbours include the Saudi royal family and the Brunei royal family.

The squatters have been told that the property is worth £30 million. Trevor Abrahmsohn, of Glentree Estates, the estate agent responsible for some of the biggest sales in The Bishops Avenue, agrees with that valuation. Mr Abrahmsohn told The Times: “The land that the house is on has planning permission for a 50,000 sq ft property to be developed. I would not be surprised if it were worth £30 million.”

Calin Ciufudean, a 32-year-old “professional” squatter, said that the owners, who could not be traced last night, know that the squatters are in. However, he claims that they do not mind because he and his housemates are “looking after” the home by carrying out repair works and gardening.

Mr Ciufudean said: “It was in a horrendous state when we found it. It wasn’t good enough for anyone to visit, let alone to live in. There was no air, leaks and mushrooms and mould growing. We had to wear masks.”

He said that he and his friends had embarked on a renovation project, removing all the carpets, throwing away rubbish and doing the gardening, but that “a lot still needs doing”.

Mr Ciufudean, who recently set up Prep Ltd, a company offering property management services to absent owners, said that he would stay until the owners decided whether to sell up, develop the property or demolish it.

The details have emerged amid growing concern about the number of properties left empty in Central London by rich owners, presenting a golden opportunity to squatters.

According to the Empty Homes Agency (EHA), there are about 80,000 empty properties in London, or 2.5 per cent of all homes. A growing number are properties bought by foreign investors who want a secure asset but continue to live elsewhere.

David Ireland, chief executive of the EHA, said: “We have noticed a number of Middle Eastern, Russian and South African owners buying property, then leaving it empty. Very often this is seen as a legitimate use, but occasionally, it seems to be funny money.”

Mr Ciufudean said: “To have a property like this empty is such a waste. We are trying to make the squatting experience a good thing by looking after it on behalf of the owner.”

Latest figures from the EHA show that the number of empty properties in Westminster, which includes Mayfair, Belgravia and Marylebone, stood at 3,584 at the end of 2008. For the London Borough of Barnet, which includes The Bishops Avenue, the figure was 3,627.

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