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Code breaker Herbert Yardley 'betrayed UK'

16 September 2013 Last updated at 10:18 BST

The American code breaker, Herbert Yardley, is buried in Arlington national cemetery in Virginia and remembered in the US as a hero.

For more than 10 years after the end of World War I, Yardley was the head of an American government unit credited with breaking Russian and Japanese diplomatic codes.

But new evidence unearthed by Radio 4's Document programme suggests he may in fact have betrayed his nation by helping the Japanese to crack secret British and American codes during World War II.

The Today programme's Mike Thomson reports.

First broadcast on the Today programme on Monday 16 September.