"I like being old at least as much as I liked being middle aged and a good deal more than I liked being young," writes author Jane Miller in her book Crazy Age, but it’s a quote one can eventually imagine being attributed to any of the people profiled on 56 Up too.

This remarkable documentary series, which has been screened every seven years for almost half a century, has become essential viewing since it returned last week to catch up with the children first profiled by filmmakers Paul Almond and Michael Apted in 1964, who are now entering middle age.

And in an era of ten-a-penny ‘reality’ formats like Big Brother, which showcase bizarre social experiments rather than real life, it’s refreshing to see the lives of ‘normal’ people played out on screen.

Masterfully painted through a combination of highlights of previous Up documentaries and new footage, 56 Up is not, as Nick Hitchon pointed out last night, an “accurate picture” of any of one of the participants, but a broad and captivating portrait of human experience.

Triumphs, tragedies, successes and regrets; the series brings into focus the lives of people from all walks of life, ranging from those born with a silver spoon in their mouths to people raised without even knowing who their parents were.

But far from being a depressing look at dreams crushed underfoot while the brow wrinkles, 56 Up ultimately leaves viewers with a sense that life does, indeed, get better with age.

Yes, some of the show’s participants have had lives blighted by poverty, mental illness, bereavement and divorce, but the overriding tone of their stories at 56 is one of healing, acceptance and contentment.

While the participants may not have achieved greatness outside the documentary (as Nick says, “I wanted to be known for science and not just for these films, but that’s not going to happen”), the one trait they all seem to share as they age is a growing sense of positivity.

From troubled Neil Hughes, who at 56 seems much more contented than his homeless 20-something self, to stoic Jackie Bassett who has endured myriad personal tragedies and setbacks but remains “cheerful”, these are people who’ve lived very different, but ultimately fulfilling lives.

It’s occasionally sad to see footage of the seven-year-olds full of naïve hopes and dreams contrasted with their grown-up selves, resigned to reality. But it’s the ability of each of these people to make the best of things that makes 56 Up truly inspirational.

These days, people seem to see an appearance on TV as a panacea for life's ills; the individuals queuing round the block to audition for the X Factor imagining that a personal experience of Warhol’s 15 minutes of fame will somehow solve all their problems. Yet 56 Up shows us that this isn’t so: these people aren’t contented and well-adjusted as a result of being on TV – they’ve achieved their sense of calm in spite of it.

For anyone with an interest in social history or even just a nosey desire to know more about the lives of others, 56 Up is truly compelling viewing that leaves one with a sense that, as Jackie’s teenage self put it, while you can’t be happy all the time, you can still find happiness.

Part 3 is on ITV1 on Monday 28 May at 9:00pm, you can catch up with the current series on ITVPlayer, and you can see the previous Up documentaries on YouTube.