Campaigners fighting for a museum for Holocaust education at Trent Park to honour the site’s secretive role in winning WW2 and uncovering Nazi atrocities have blasted the developer’s “pitiful” offer of space.

Alongside Bletchley Park, the north London mansion helped British spies win the intelligence war, housing high-ranking German officials and gathering vital evidence – including of Nazis’ mass killing of Jews.

After a showdown public meeting last week, historians warned that inadequate space would rob future generations of a unique opportunity to learn about how the horrors of the Holocaust came to the attention of Britain.

Author Dr Helen Fry said: “We must give the Trent Park Museum the full space that it needs… You can’t tell the story properly with a couple of broom cupboards next to a café. We want at least one room on the significant discoveries of the Holocaust.”

Berkeley Homes, the new owner of the former Middlesex University Campus site, want most of it for luxury housing, developed over 45,000sq metres (52 acres). The company is offering 500sq metres for “ancillary uses”.

Fry, together with campaign director Jason Charalambous and historian Damian Collins MP, are demanding half the stable block, and the whole of the ground floor and basement of the mansion house “as an absolute minimum”.

Berkeley’s chairman Tony Pidgley said the company “has a great track record of developing sites of historic significance in a sensitive manner,” but Charalambous said the offer was “a pitiful amount that does not do justice to the estate’s significant national history”.

The campaigners’ argument was supported by Iain Standen, the chief executive of Bletchley Park, where Alan Turing and his team famously broke the Enigma code to turn the war effort in the Allies favour.

Bletchley now sees 250,000 visitors annually, and Standen said Trent Park also had the potential to become a significant national attraction, because it “has a unique and engaging story, which means people will come to visit”.

A petition for the museum, which had attracted almost 1,500 signatures this week, notes that Trent Park used “highly sophisticated room-bugging, eavesdropping and passive manipulation techniques,” on the dozens of high-ranking Nazis housed there.

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Berkeley Group have offered to digitise and release old wartime footage included in the sale of the Trent Park site

After documents were declassified in 2004, historians discovered that the precursor to MI6 operating at the site learned about German U-boat tactics, radar technology and Hitler’s secret weapons programme, including the V1, V2 and atomic bombs.

Crucially, they also began hearing more details about the mass killing of Jews, as German generals casually discussed it without realising they were being recorded.

Fry said: “We began hearing about Nazi atrocities at Trent Park in 1940, at every stage, leading up to the Final Solution. They were detailing things like mobile gas trucks. By 1943 they Germans were already talking about 3.5 million Jews killed. Future generations should be able to come here and learn about this. It’s really important to do it justice.”

The Berkeley Group said: “Our vision for the site has been shaped by an extensive consultation process, and is driven by our goal to secure a long term legacy for the site. We will continue to work with the campaign.”