Bletchley Park code-breaker Professor Donald Michie, 84, and his ex-wife, geneticist Dame Anne McLaren, 80, were killed in a car crash this Saturday.

Their son, Jonathan, told Reuters that his parents were travelling from Cambridge to London on the M11, when their car left the road and hit a tree. No other cars are reported to have been involved in the accident.

Both were extremely eminent scientists: Dame Anne was the first female officer of the Royal Society, a fellow of King's College and Christ College, Cambridge, and a member of the Warnock Commission, an ethical advisory board on the use of genetics. Her ex-husband Professor Michie was an artificial intelligence researcher who had worked with Alan Turing at Bletchley Park during the second world war.

Martin Rees, president of the Royal Society, said that Dame Anne's death was a "great tragedy and a loss to science... She was both idealistic and effective, and her loss will be deeply felt not only by her fellow researchers, but far more widely."

It was at Bletchley Park that Professor Michie developed an interest in machine intelligence, but it was an interest it would take him some time to revive.

After the war he went to Oxford to study medicine, going on to obtain a D Phil in Mammalian Genetics. He worked in Zoology, briefly alongside Dame Anne at UCL, until the mid 1960s, when he returned to his programming roots and set up the Experimental Programming Unit, at the University of Edinburgh. There he later founded the Department of Machine Intelligence and Perception.

Professor Michie's work at Bletchley Park contributed to cracking Tunny, a German teleprinter cipher implemented by the Lorenz machine. The code breakers never saw a Lorenz machine until after the war, but they had been decoding its messages for two and a half years.

The Lorenz machine took a stream on input and obscured it using the Vernam system. This took a plain text message and added an set of obscuring characters to it, producing the cipher text. The same set of characters could then be added back to the cipher text and would reveal the original message.

The original German plan was to use characters from a one-time pad to encipher the plain text, but this proved operationally difficult to manage. As a result, the obscuring text was provided by a pseudo-random number generator. The pseudo in the random was the chink in the armour that allowed the team at Bletchley to break the cipher.

According to Jonathan Michie, at the time of his death, his father had been preparing to give a lecture on the history of machine intelligence to the University of Edinburgh.

The couple worked together at University College London during the 1950s. They were married in 1952 and had three children before divorcing in 1959. Despite the breakdown of their marriage, they remained close and still shared a house in Camden, North London.

Professor Michie also leaves another child from an earlier marriage. ®