The fortress-like 1960s concrete block housing America’s embassy in Britain could be listed by English Heritage.

The conservation quango is expected within the next few weeks to recommend to Andy Burnham, the culture secretary, that he should give the 600-room building a grade II listing.

The US ambassador, Robert Tuttle, is said to have been lobbying the conservation quango to head off the preservation order, which could halve the estimated £200m value of the embassy in Grosvenor Square, Mayfair.

Under the proposed listing, reported in the Art Newspaper, any alteration to the embassy, built in 1960 to designs by the Finnish-born American architect Eero Saarinen, would have to be approved by English Heritage.

Tuttle – once described by Ken Livingstone, the former London mayor, as a “chiselling little crook” when his embassy refused to pay the congestion charge – had been planning to move out of the building, but those plans may now have to be reconsidered.

Neighbours are also angry that a building that many of them see as a monstrosity will be protected. They had hoped it might be knocked down when the embassy moved out.

“This is not a straightforward case,” said Robert Davies, head of planning at Westminster council. “English Heritage know there are political implications. They are dealing with the American government . . . Who is going to buy an embassy building you can’t touch?”

Unlike the current dispute, in which it finds itself on the same side as locals, the embassy has previously made enemies with the maze of security barriers it introduced after 9/11. Those are now likely to stay even longer.

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