Serial squatters have taken over a house in the same Belgravia square that is home to Nigella Lawson and her art collector husband Charles Saatchi.

The group, known as the "Belgravia Squatters", moved in to the palatial six-storey home in Eaton Square.

They had been evicted from a seven-storey, 42-room property near the home of the King and Queen of Jordan in nearby Eaton Place the previous day.

The new squat, thought to be worth up to £33 million, was once owned by the Amery political family and played host to politicians and diplomats.

The squatters gained access to the property legally through an open first-floor window. They pinned a notice on the door, stating their squatters' rights and warning against interference.

Their spokesman, filmmaker Mark Guard, 45, said: "This is yet another abandoned property owned by someone hiding behind an offshore account. There is seven years of post piled up. The police evicted the squatters from the last place and when they throw them out of this property, there is another one lined up around the corner.

"If owners continue to abandon these mansions without securing and looking after them, they will be squatted in. There are hundreds of properties like this in Belgravia and they are all targets. The squatters are doing this legally and have not damaged any properties." Mr Guard said owners should offer properties to key workers struggling to find accommodation. He added: "They will babysit these properties for the owners. There is no reason to leave them empty and falling apart."

The mansion has 34 rooms and, although dilapidated after being empty for years has elegant carved mantelpieces, cornices, ceiling roses and painted designs.

In 1940, it was where prime minister Neville Chamberlain's fate was sealed when Leo Amery, a Tory minister, held the meeting in which the party ditched him in favour of Winston Churchill.

After the six-day war in 1967, King Hussein of Jordan and Moshe Dayan, the Israeli defence minister, came to the house - known as "the unofficial foreign office" - to secretly discuss peace.

Six years ago, the property was said to be worth less than £10 million but a similar-sized house in the fashionable square recently sold for £33million.

The Standard has revealed that squatters are regularly targeting properties worth up to £50 million in Belgravia and Mayfair, which are often owned by investors hiding their identities behind offshore companies.

According to the Empty Homes Agency, there are more than 80,000 empty properties in London, 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.

Eaton Square is among the most prestigious addresses in London. Lawson and Saatchi live in a sprawling mansion complete with its own library and huge reception rooms.

Football managers Jose Mourinho and Sven-Goran Eriksson have also lived there.

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