The BBC's Lisa Costello: "It was just known as the 'hush-hush' place"

After seven years of negotiations, the owners - BT and the government land agency Pace - have finally agreed to a plan which is intended to preserve both the historial legacy and financial wellbeing of the Buckinghamshire site.

The Bletchley Park Trust now has a 250-year lease on half of the grounds and all the buildings of what used to be known simply as Station X.

But this will not be a theme park with "white knuckle" rides.

The trust's chief executive, Christine Large, said the overall theme would be the science of communications, particularly secret communications.

'Goose that laid the golden egg'

"This is based firmly in the heritage of Bletchley Park and its role in World War II intelligence computing and cryptology," she said.

The massive wartime contribution of Bletchley Park and its staff of mathematicians, crossword experts and linguists only came to light in the 1980s when the government declassified secret papers.

Enigma: Breaking the code shortened the war

Codebreakers working at Station X cracked the much-vaunted German U-boat cypher, Enigma.

Some historians say the breakthrough shortened the war by several years and was one of the most vital contributions to the Allied war effort.

It was said that because of the skill of the Bletchley codebreakers Winston Churchill used to read Hitler's messages before the Führer.

The ultra-secret Bletchley Park was described by Churchill himself as "the goose that laid the golden egg, but didn't cackle".

The theme park will save the site from a planned commercial redevelopment. Eight years ago the historic buildings were earmarked for demolition.

£1.5m kickstart

But the theme park plan is only the beginning, rather than the end of the battle to save Bletchley Park.

The Trust must raise £1.5m in its first year to kickstart its development plans, and needs to find a total of £20m to complete the job.

US computer billionaire Bill Gates has reportedly been approached for sponsorship.

Author Robert Harris, who immortalised the Bletchley Park story in his best-selling novel Enigma, says Mr Gates would be an ideal sponsor.

British mathematician Alan Turing, widely acknowledged as the "father of computer science", worked at Bletchley Park during the war.

Hollywood apology

The story of Station X is being turned into a controversial £90m Hollywood blockbuster.

The film's makers caused outrage when it was discovered that Americans were accredited with capturing the Enigma machine.

In fact the machine was seized by the Royal Navy.

Lieutenant Commander David Balme RN, who led the operation, was offered a part in the film as an apology.

A postscript to the film will note the Royal Navy's role in the capture.