BRITAIN’S spy agency GCHQ had a 30-year colour bar that was only abolished around 1980, according to its first authorised history. 

Bletchley Park’s discriminatory past was unveiled in a new book published today, in which author John Ferris was given unprecedented access to secret files. 

Sifting through 100 years worth of documents, Mr Ferris found that GCHQ had taken “active measures” to avoid employing non-white staff.

“I think it is essential that I did a warts-and-all account and GCHQ, to its credit, was willing to let me do that,” he said. 

He said that some of the things he found “they wish hadn’t happened.” 

“For example, there is a ‘colour bar’ in employment in GCHQ in the 1950s and ’60s.

“In other words if you’re not Caucasian, they don’t want you in. And they take active measures to avoid hiring you.”

The historian said that the same discriminatory practices were also in place at other British intelligence agencies during that time.

GCHQ was established on November 1 1919 as a “cryptanalytic” unit. During World War II, staff were moved to Bletchley Park, Buckinghamshire, to decrypt Nazi Germany’s messages, most notably those sent from the Enigma encyption device.

In June 2013 the US whistleblower Edward Snowden revealed that the spy agency had been collecting communications sent over the internet on an industrial scale. 

Earlier this year Amnesty International launched a legal case against the government over its mass surveillance programme, claiming it had also been used to spy on human-rights organisations.