The Grade I listed building, built by Robert Adam in 1770 off Portland Place, served for half a century as the Austro-Hungarian embassy and featured in the film Sense and Sensibility. But in more recent years it has stood empty and has been ravaged by dry rot.
In May this year, English Heritage took the rare step of issuing a compulsory purchase order for what had become one of the most important buildings on the quango's "Buildings at Risk" register.
A public inquiry was to be held next month. But following a start on repairs by the owners, Fairgate Investments, the inquiry has been adjourned indefinitely.
The property company, chaired by a Nigerian chieftain, Chief Akindele, has put a new roof on the building and has agreed to begin further work in the new year. This will include replacing four ornate Adam chimney pieces which were stolen last year.
Sir Jocelyn Stevens, chairman of the heritage quango, said he was relieved that work was at last in progress, but added that the CPO would not be withdrawn until it was completed.
Last May he railed against the "disgraceful neglect" of Chandos House. Extensive dry rot threatened to spread into the principal rooms and there were cracks in the wall.
Fairgate bought the property for pounds 6m in 1988 at the height of the property boom, intending to turn it into a hotel. But, as the company's solicitor observed yesterday: "My clients bought the wrong property at the wrong time." Once repaired, the house will be put back on the market for residential or hotel use.
Built for the third Duke of Chandos, the house became the Austrian (later Austro- Hungarian) embassy from 1815 to 1871 and was the scene of glittering parties hosted by Prince Eszterhazy, the ambassador. Its most recent occupant was the Royal Medical Association. On film, it was also the home of John and Fanny Dashwood in the film of Jane Austen's Sense and Sensibility.
Fairgate successfully settled a legal action against a security company over the theft of the chimney pieces. Replacing them will be a specialist task involving the import of marble from Carrara in Italy.
English Heritage served a repairs notice last February, giving the owners two months to carry out pounds 900,000 of work.Reuse content