Parts of the telephone exchange have been described as being in a "very bad" condition
A "secret" underground telephone exchange has been included on a list of buildings at risk from neglect.
Parts of the Burlington Bunker, near Corsham in Wiltshire, have been included on Historic England's At Risk Register, external for the first time.
The Prime Minister and 4,000 government personnel would have been relocated there in the event of a nuclear war.
The site remained secret until 2004. Parts of the exchange are described as being in "very bad" condition.
Nick Croxson from Historic England said: "Because it's underground there are problems with damp.
The underground site would have been used by government staff in the event of a nuclear war
"We've been working closely with the Ministry of Defence (MoD) over several years to try to install dehumidifiers."
Mr Croxson said a partnership agreement between Historic England and the MoD was being set up to set out a framework of how to manage the site in future.
The rooms, which are part of the Corsham Tunnels, are 100ft (30m) underground and were adapted to a government facility in the 1950s.
The damp conditions underground have led to damage to some of the features
The massive complex was designed to safely house up to 4,000 central government personnel in the event of a nuclear strike.
In a former stone quarry and codenamed Burlington, it was to be the site of the main Emergency Government War Headquarters - the hub of the country's alternative seat of power outside London.
Historic England's register provides an annual snapshot of historic sites known to be at risk from neglect, decay or inappropriate development.
The telephone switchboards at the site have never been used
- Published20 October 2015
