GCHQ doughnut lit up in rainbow colours
The GCHQ "doughnut" building in Cheltenham is to be lit up in rainbow colours as a symbol of the intelligence agency's commitment to diversity.
It will take place later, to mark International Day Against Homophobia, Transphobia and Biphobia.
Computer pioneer and codebreaker Alan Turing kept his sexuality a secret while working at Bletchley Park, GCHQ's forerunner, during World War Two.
His nephew, Sir John Dermot Turing, said he was "delighted" by the gesture.
A spokesman said the rainbow illumination demonstrated GCHQ's pride in its diverse workforce.
Until the early 1990s, being openly gay was a bar to employment there.
Attitudes have changed over the past 20 years, and now diversity is not merely accepted at GCHQ, but is actively promoted in its workforce, a spokesman said.
Sir John said: "My uncle made a crucial contribution to the safety of the nation when he worked for GCHQ's forerunner... but due to society's attitude at that time he was forced to hide his sexuality.
"It is important that his successors at GCHQ today are free to be themselves, and therefore bring their talents to such vital work."
Alan Turing studied mathematics at Cambridge University, and much of his ground-breaking work in computing was conducted at the University of Manchester.
It was in the city, in 1952, that he was arrested for having sex with another man, which was then an illegal act.
Director of GCHQ Robert Hannigan said: "World-leading innovation in technology absolutely requires diversity.
"That was true for GCHQ when Alan Turing tackled Enigma for us and it is just as true today.
"I'm proud of our diverse and creative workforce."