Trent Park, a stately home in north London, will soon be developed into luxury homes. But during World War Two, this grand red-brick building housed one of the most secret and significant British intelligence operations.
And historians and local politicians say a substantial part should be preserved as a museum.
Nearly 60 captured German generals were held at Trent Park, their conversations secretly monitored and recorded. There were even microphones hidden in trees to catch their exchanges as they strolled through the extensive well-tended park, part of it planted with a million daffodil bulbs - creating a vast white and yellow lawn in front of the house every spring.
Trent Park was one of three World War Two eavesdropping centres and, campaigners say, the only one which could now be turned into a museum or memorial.
Every waking minute
Fritz Lustig, now 97, is one of very few surviving "listeners" (German speakers working for British intelligence), who monitored the conversations of prisoners of war.
He worked at the other two centres, Latimer House and Wilton Park, both in Buckinghamshire. He strongly supports a museum at "Cockfosters" - the codename for Trent Park during the war.
Mr Lustig told me that listeners had to keep an ear across everything the Germans said - from the moment they woke until they went to sleep. The conversation was only recorded when it touched on certain sensitive topics. Then the listeners would switch on the gramophone.
In all, according to historian Dr Helen Fry, at least 100,000 such conversations were recorded and transcribed in full and have been kept in the National Archives.
Mr Lustig doubts the Germans knew they were being bugged. "They weren't very security conscious," he says. "The microphones were very good though - even when they turned the tap on to drown the conversations, we could still hear the words."
'As important as Bletchley Park'
The eavesdropping was kept secret for decades. The listeners had all signed the Official Secrets Act and many received no acknowledgement of their work, nor understood its importance. The last official papers were only declassified 12 years ago.
The records show important information was gleaned this way including, from Trent Park, early warning of the V1 and V2 rocket projects.
Dr Helen Fry argues it is as important a site as Bletchley Park, the secret code-breaking centre, and must be preserved as a museum, explaining the work of the secret listeners.
"There is nowhere else in Britain where we could have this," she says. "The other two sites - all the other World War Two stuff has disappeared. On one site, even the stately home has been demolished."
She is helping to lead a campaign to set up a significant part of the building as a museum, asking the building's new owners Berkeley Homes to give up the grand rooms in the ground floor and the basement.
"We can recreate, for example, the office of the camp commander. We can restore the stairs to the basement and show the world of the secret listeners there - with all their spy gadgets," explains Dr Fry, author of The M Room: Secret Listeners who bugged the Nazis.
She suggests that the spacious high-ceilinged rooms on the ground floor could be furnished and decorated to show the comfortable lifestyle the German officers enjoyed, rather like a country club. Those who ran the centre believed the more relaxed the prisoners were, the more unguarded their conversation.
Trent Park House
- Grade II-listed mansion in Enfield, north London
- During World War Two, captured German officers were held here and their conversations secretly monitored
- After the war it was converted into a college, first as Trent Park College of Education, which became part of Middlesex Polytechnic, now Middlesex University
- Sold to Malaysia's Allianze University College of Medical Sciences for £30m in 2013
- Acquired by Berkeley Homes in 2015
Museum... or cafe?
Both Dr Fry and local councillor Jason Charalambous suggest Trent Park could be developed like Bentley Priory, another north London stately home with World War Two significance.
Bentley Priory was the headquarters of the RAF for the Battle of Britain. Though few artefacts remain, a good part of the building has been turned into a museum. The rest is private housing and there are new homes on the grounds.
Berkeley Homes, which acquired the Trent Park site last year, has expressed interest. Its representatives have been meeting local campaigners and held a public consultation. They have promised to restore the building, which has had little investment for many years, and the famous gardens and grounds.
The company told the BBC it wants to work "in partnership" with the local authority and community. However, it has not yet published its plans for the site.
Dr Fry and Mr Charalambous fear the "museum" could end up as a cafe and "just a few panels in a tiny corner of the house".
Listen to Sanchia Berg's report on Today on Radio 4 on Tuesday, 12 April.