(Photograph) - If you cannot find the time to write up your PhD why not leave it until you are less busy - for instance in your seventies? Holly Clyde Wagner found he had too many interruptions during his working life but he has just finished his PhD in geology, from Leicester University, at the age of 76.

Dr Wagner came from California to resume two years of geological studies that he had dropped 40 years ago at the University of Kansas in Lawrence.

His supervisor, John Hudson, said: "He has had a long and rather distinguished career within the United States Geological Survey. If you were judging him as a person you could have given him a PhD on sight.

"I think he felt frustrated. He had obviously invested a lot of effort in the 1950s. And in science the PhD has become the expected minimum qualification: perhaps he felt a bit naked without one."

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Dr Wagner worked both in the US, where he had an external supervisor who was connected with Leicester University, and in the UK, where he spent three summers studying at Leicester spread over six years. Professor Hudson says: "Our regulations about part-time PhDs are fairly liberal."

Dr Wagner says: "Both my wife's family and my own family originally come from England and Scotland, so going to Leicester was a good opportunity to explore Britain."

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Over the next few years he hopes to carry on writing reports and also to develop his PhD work.

But Professor Hudson is not looking to develop the trend of PhDs in retirement. "The whole thing is a complete exception."