Legal action may be taken to save an historic former hospital if the owners do not prevent its deterioration.

Richmond Council’s planning committee approved a proposal from Diligent Finance for 89 homes on the site of Normansfield Hospital, in Hampton Wick, in January 2008.

Approval came after permission was granted to Laing Homes in 2001 for 190 new homes and a 49-bedroom hotel on the Grade II* listed hospital site.

The hotel was never built and the land was sold to an offshore company, before Diligent lodged the application to restore the hospital, but put extra homes on the site.

The authority said last week it was extremely concerned about the state of disrepair of the property and the appearance of the site, which is within a conservation area and is on English Heritage’s at risk register – which seeks to identify the parts of the nation’s historic environment that are endangered, and to get something done about them.

A spokesman said the council had reminded Diligent it is expected to maintain the building in a sound, secure and weather-tight condition, and has powers to undertake urgent works necessary for the preservation of the building – it also has powers to force the owners to remove graffiti and tidy its land, when this is detrimental to the amenities of the area.

He said the council had called for an urgent meeting with the company to move the situation forward, but had yet to receive a response.

Councillor Tony Arbour, who represents Hampton Wick on Richmond Council, urged the authority in April to take strong action and said the building was “too important to be left to fall down or be a pawn for property speculation”.

“The condition of the building, both inside and out has gone from bad to worse,” he added. “Vandals have free access and each day the cost of restoration rises.”

Philip Wealthy, head of planning policy and design at the council, said: “We will use legal powers, if necessary, to ensure it is not allowed to deteriorate.

“The council also recognises residents’ concern that the appearance of the site needs to be maintained in a satisfactory state, and again will seek to reach agreement with Diligent Finance.”