LONDON: The Bank of England on Thursday unveiled a new design for Britain's top-value banknote featuring gay World War II code-breaker Alan Turing, celebrating diversity even as cash falls out of favour.

The more durable and forgery-secure £50 polymer note (worth about $70 or 60 euros) will enter circulation on June 23, Turing's birthday, the UK's central bank said.

Turing was a mathematician and is considered the father of modern computing. He spearheaded a team at Britain's Bletchley Park that cracked the Nazis' Enigma code in 1941.

"He was also gay, and was treated appallingly as a result," Bank of England governor Andrew Bailey said in a statement.

"By placing him on our new polymer £50 banknote, we are celebrating his achievements, and the values he symbolises."

The Cambridge University educated mathematician also developed the "Turing test", which looks at what criteria are needed to judge whether a machine can think like a human -- the foundation for artificial intelligence.

But he was prosecuted in 1952 for "gross indecency" and was forced to undergo chemical castration as an alternative to jail.