When Seven Up first aired in May 1964, it featured 14 very different seven-year-olds, all revealing their thoughts and aspirations to the camera. The prep school boys were already eyeing Charterhouse and Cambridge. East Ender Lynn Johnson wanted to work in Woolworths. The curveball was Neil Hughes, a moptopped little Liverpudlian who announced: “I want to be an astronaut.”

The title of that first series came from an old Jesuit saying: “Give me the child until he is seven and I will give you the man.” The seven-yearly series returns this week with 63 Up. Did Hughes make it into space? “You know what kids are like,” he laughs as we meet for coffee at a hotel in Penrith, Cumbria. “If they’d filmed me a week later, I might have said something completely different.” The moptop is gone, too.

While the posh boys became barristers and Johnson a librarian, the Up cameras tracked Hughes’s dramatic experiences with depression, squats, homelessness and destitution. And then 42 Up revealed his remarkable transformation into a Liberal Democrat councillor and a lay preacher. (He also stood, unsuccessfully, at the 2010 general election.)

Although his ups and downs have gripped viewers for decades, Hughes is keen to point out – genially – that Up is very much director Michael Apted’s “interpretation” of his life. “For most people,” he says, “what’s on TV is more real than the truth. But people must remember that there’s someone behind the camera.” Hughes stopped watching the series after 21 Up. In fact, he virtually stopped watching TV altogether. “People tell me I’m portrayed as triumphing over the odds,” he says. “But that’s not how I see my life at all. I’m grateful for the successes, but I see my life ultimately as a failure. I’ve failed in almost everything I’ve tried to do.”

He describes himself as “reclusive” and “a bit eccentric”. He doesn’t own a mobile phone and finds modern society baffling: “How can anyone want to spend their time tapping away on a device?” But he was so keen for the world to hear his side of his story that he penned an autobiography: it exists in a single, unpublished hard copy. “It’s my truth, in case anyone is interested.”

So what did happen to that gentle, hopeful little boy who charmed a nation by skipping happily to school? Picked for Seven Up for his enthusiasm and opinions, Hughes, the son of two teachers, says he had a happy childhood, though not quite as idyllic as depicted. “We had family arguments. You’d go on holiday all cheerful and come back in a silent car.”

In 14 Up, however, he was agitated and complained of being unable to relax. “I went to a rough school and got bullied a lot,” he says. “I got beaten up several times and, to be fair, I beat people up as well.” At the age of 16, he was diagnosed with a “nervous complaint”.

He adored literature and, after reading Brideshead Revisited, dreamed of going to Oxford. He got the required grades but flunked the admission exam. “I think I misquoted someone,” he sighs. It haunted him for years. He spent six months hitchhiking to toughen himself up. “When I think of the risks I took, the places I stayed, the people I associated with, I swallow hard.” He ended up at Aberdeen university, studying languages and law when Scottish nationalist students mounted what he calls a “soviet-style takeover” of student halls. “If you were not Scots, then woe betide you. Nobody threatened me, but it was a horrible atmosphere.”

Dropping out after the first term, he slid into years of menial jobs and life on benefits, to the chagrin of his father. He worked in hotels and as a grouse-beater. “You don’t actually beat the grouse,” he laughs, and I realise that the Up cameras have not done a great job of capturing his warm, dry sense of humour. “But if they were half-killed, then you had to wring their necks. As a teenager you don’t care, but later you think, ‘What am I doing to serve the planet?’”

In 28 Up, he was homeless in the Highlands, sleeping in sheds, while 35 Up found him on a council estate on Shetland, visibly struggling with his mental health, but he says it wasn’t quite the torrid time the show presented. “When I got there, a quarter of the community had no television,” he says. “But being completely isolated, you learn to depend on the few people who are there, and also to be more robust.” He read avidly, overcame his rejection of religion and realised the power of community. “I knew I had to go into politics. Shetland changed me as a person. And the northern lights – spectacular!”

By 42 Up, everything had transformed again, thanks to another Seven Up participant. In that very first series, boarding school boy Bruce Balden said he wanted to help poorer people. After seeing Hughes’s struggles, his adult version – who had taught in Bangladesh and London’s East End – reached out, putting Hughes up at his home in London, then finding him a basement flat in Hackney, where he finally obtained a degree via the Open University. “Bruce was a great help,” Hughes smiles. “I couldn’t hold down a job, but I wanted to contribute to society.”

When he first went along to Hackney Lib Dems, the “ruthlessness” shocked him. “One guy would stop at nothing to get what he wanted,” he says. “I didn’t think I was tough enough for that world, but when we knocked on doors my experiences meant I could chat to anybody, whatever their situation. I didn’t have to make anything up.” Finally, tiring of London politics, he visited friends in Cumbria – a childhood holiday haunt – and stayed, eventually swapping his caravan for a housing association cottage. “Politics is very different here,” he says. “I enjoy helping people, empowering communities.”

These days, he divides his time between his councillor duties, the church and voluntary work in an Oxfam shop. This week’s 63 Up reveals that he got married – to a woman he met in panto – but after four years the relationship ended, owing to his recurring low moods. “I’ve still not got over that.”

His parents have died, too, but there had been a reconciliation. “I got on better with my mum when she had dementia,” he says with a sigh. “All my life, she’d been trying to mould me into something I wasn’t. But by the end she seemed to accept the way I was.” Hughes seems to view his own life as one of shattered dreams. “If I’d been successful, I’d have been in Westminster, stopping this hideous government or I’d be in theatre, directing what I wanted.”

That said, he recently helped to get rid of a “rubbish council”, is campaigning passionately to restore the Keswick-Penrith railway line – and he still dares to dream. “If you can change the neighbourhood you live in,” he says, “you can change the world.” His eyes are sparkling, just like the eyes of that would-be astronaut back in 1964.

63 Up is on ITV at 9pm on 4, 5 and 6 June.