The US government is in talks to sell its Mayfair embassy in London to Chelsfield Partners, a property investment company backed by Qatar Investment Authority.

The group has emerged as a favourite to secure the sale of the imposing concrete building – with its distinctive golden eagle – in Grosvenor Square, which has more than 200 years of association with the US government.

Final negotiations about price and rents are still progressing, with the block thought to be worth between £300m and £400m.

Other parties interested in the sale have been informed they have not reached the next round.

These include the Duke of Westminster’s property company Grosvenor, which was in partnership with Qatari Diar, and Hines, the company run by veteran US property developer Gerald Hines.

Financial Times