Britain's first glimpse of Nicholas Hitchon in Seven Up! was as a tiny boy in Wellington boots, striding confidently along a Yorkshire country lane. When we meet him again next month, in the eighth instalment of what has become a TV landmark, he'll be 56 and back in the Dales.
The films, voted the greatest-ever documentaries in a 2005 poll, started charting the lives of a group of seven-year-olds in 1964. Now programme-makers have been back to check their progress at seven-year intervals over almost five decades. During that time Mr Hitchon has gone from his one-room Yorkshire village school, where he was keen to "find out about the moon and all that", to Oxford University and a successful academic career in America. The last time we saw him in 49 Up, he was in the US working as a professor in the University of Wisconsin-Madison's electrical and computer engineering department and being interviewed with his second wife, Chryss.
Mr Hitchon revealed this weekend that little has changed since that broadcast, but said it was refreshing to return to his birthplace for the filming of 56 Up, overseen – as all but one of the series has been – by the director Michael Apted.
Recalling the approach from the documentary-makers after the most recent seven-year break, he said: "I knew they were going to show up. The most fun part about this one was that I go back to the Dales, which was great. And we got to talk about how it was when I was a kid. They said, 'We did America last time, let's do the Dales this time.'"
One of the issues that Apted reflects on in 56 Up is the way Britain has changed. "Michael asked us about how education had changed, because people are borrowing money to go to university now," Mr Hitchon said. "In our day, none of us paid for our education. England's also changed a lot. For instance, no one is farming the Dales any more and there are all these multimillion-pound houses. I don't know what England's like any more. I've been away for 30 years."
Apted also revisits the theme of success. "If you're still hanging in there and swinging punches then you're a success," said Mr Hitchon. "Does that apply to me? Sure, why not? I'm working all the time to solve problems that I think are important. I'm hanging in there despite the fact that it doesn't all go the way you hope."
He is one of a handful of the original 14 children to have appeared in all instalments of the series, although he says as far as he knows most of them will return for 56 Up.
While committed to the project, he says confessing all in front of the camera has never been easy. "It's always very disturbing. It's the fact that they don't show you the way you want to be shown – but that's not the main thing. They ask you some really disturbing questions. They stick a camera under your nose and ask – 'Why did you choose your wife?' – and then it's shown to gazillions of people. I've learnt that the stupider the thing I say, the more likely it is to get in. You're asked to discuss every intimate part of your life. You feel like you're just a specimen pinned on the board. It's totally dehumanising."
There were often times when his relationship with Apted was strained, particularly because of the director's merciless interviewing style. "Michael is an Englishman of a certain generation, so he's very reserved. He's all business and he just wants to make a great film."
The professor said 28 Up caused particular friction. He had just moved to the US with his first wife. On the film's release, he reacted angrily because he felt he was portrayed as someone who hung out in shopping malls and moved to the US for money. "Anyone who knows me knows that I don't hang out at malls," he said. "But [Apted] took me to one and filmed in front of a lot of girls' punk clothing and said, 'Nick came to the US for a salary of £30,000'. Some people in England changed their mind about me as a result, thinking what a jerk he's become. That was really upsetting."
Regardless of such unhappy episodes, he says he has never considered pulling out of the series. Primarily, he thinks the documentaries are important for the unprecedented way they show human lives unfolding. "It's wonderful that someone had this new idea and I feel very privileged to have been part of it – but it's come at a big cost."
If there is any uncertainty about the future of the Up series it lies with Apted, who is 71. "If Michael's still well enough, there will be more. But that's the big question – is Michael going to be around? Because he doesn't want anyone else to take over."
The other participants – where are they now?
Michael Apted Started as a researcher on the original Seven Up!, made in 1964 to test the Jesuit maxim "give me the child until he is seven and I will show you the man". He directed the next seven films, moving their emphasis from the political to the personal.
Bruce Last filmed in 49 Up, he was married to fellow teacher Penny and teaching at a prestigious public school, St Albans School, in Hertfordshire.
Jackie, Sue and Lynn Jackie Bassett appeared in Seven Up! with friends Sue Davis and Lynn Johnson. She was last seen living in a council flat in Glasgow. Sue is raising two children as a single parent. Lynn, who battled a brain condition and has two children, made a career as a school librarian.
Symon and Paul Symon Basterfield, the only non-white participant, and Paul Kligerman stayed at the same children's home. Symon had five children and by 49 Up had become a foster parent with his wife. Former bricklayer Paul was last seen working for a sign-making company.
John, Andrew and Charles All three boys were from a privileged background and went to the same private pre-preparatory school in Kensington, London. John Brisby became a barrister and by 49 Up was a QC with a house in London and another in the country. Andrew Brackfield became a solicitor and later married and had a family. Of the three, only he has been in all the Up programmes. Charles Furneaux, a documentary-maker, chose not to appear in the series after 21 Up, aside from a photograph of him in later programmes.
Suzy Wealthy Suzanne "Suzy" Lusk married a solicitor, lives in Bath and has three grown-up children.
Tony Working-class Tony Walker from the East End of London owns two properties, one a holiday home in Spain. He is married with three children, and he and his wife are grandparents.
Peter and Neil Peter Davies has changed from teaching to law and lives in Liverpool, where he plays in a band called The Good Intentions. Neil Hughes, who has struggled through periods of homelessness and mental illness, is now a councillor in Cumbria.