Peter Firmin’s Kent country home is idyllic. There’s a higgledy-piggledy Welsh dresser crammed with mugs, including plenty bearing a certain famous pink cloth cat’s bedraggled face. Two dogs, one very young, one very old – Tim and Pip, both Jack Russells – chase each other up and down the garden. Just the right amount of overgrown for a child to explore, the garden features a home-made tree house. Never mind children’s television, this is like something out of a novel.

The co-creator of Bagpuss and The Clangers, Firmin lives with his wife Joan in a rambling house they bought in 1960. They’re both in their 80s now and met at art college 66 years ago. The cottage is where they raised their six daughters, five of whom went to art college themselves, and it’s where Firmin filmed many of the episodes of his famous television creations with Oliver Postgate, his collaborator, who died in 2008 at the age of 83. The walls are crammed with artwork by four generations: they have 11 grandchildren and one great-grandchild.

He did the writing and I did the making. I could draw the things that he imagined

At one point the phone rings. It’s their youngest daughter, Emily. Yes, “the” Emily, as featured in the opening sequence of Bagpuss. Then aged eight; now aged 50. “That was Emily,” says Joan. A pause. “She’s going to Ecuador tomorrow.” Emily is a real person and she is going to Ecuador. This is too much.

Out of this world: Oliver Postgate and Peter Firmin filming The Clangers in 1968. Photograph: Smallfilms/Victoria and Albert Museum, London

There was a time when I was obsessed with Emily in Bagpuss (the first in a total of just 13 episodes was shown in February 1974) – the little girl who owned the “saggy old cloth cat”. I was envious of her because (a) she owned Bagpuss, and (b) she got to be in Bagpuss. In the pre-Thatcher era, there was no greater female power. Emily was who I wanted to be when I grew up – because Emily had the ultimate bragging rights to Bagpuss. And Bagpuss was everything.

A new exhibition at the V&A Museum of Childhood in London, The Clangers, Bagpuss & Co, celebrates the work of Smallfilms, the children’s animation production company that Firmin and Postgate started in 1959. The exhibition blurb claims Postgate’s voice and Firmin’s puppets are “cornerstones of 20th-century British culture and their quirky and inventive programmes shaped the childhood memories of millions”. This perhaps seems a wildly overblown claim to make in today’s world, where children have access to hundreds of channels (and millions of YouTube clips) at a swipe. But as a child of the 1970s, I can confirm that things were different then. You were conscious of the fact that television was a new thing and very special. There were hardly any programme choices, let alone any channel choice. Television-watching was treated with reverence and was, actually, a treat in itself. In those conditions, Emily was like a god.

Full steam ahead: cutouts from Ivor the Engine, another Postgate-Firmin creation. Photograph: Peter Firmin

Peter Firmin himself is an extraordinary character from a lost era, utterly charming and bumbling. “Sorry,” he says, “but Bagpuss is in the freezer at Bethnal Green.” (This is necessary for the puppet’s maintenance, apparently.) He keeps a few decoys about the place, nestling on shelves next to ancient pictures of Noggin the Nog and cartoons of the mice from Bagpuss. (All together: “We will wash it, we will brush it...” You can watch episodes of Bagpuss complete with “The Mending Song” on YouTube).

Most TV was live back then. If you saw a hand popping up there was nothing anyone could do

“Oh that stuff is all around the house… We have the Clangers staring at us in the dining room.” Sure enough when Joan serves up a chicken casserole for lunch, there’s a table covered in brand new 21st century Clangers merchandise from the recent remake of the show for Cbeebies. Some of the Clangers are microwaveable. Others light up and whistle unpredictably. The original Clangers were, of course, hand-knitted by Joan, held together inside with wire and Meccano: “I did the drawings and Joan worked out the knitting patterns from the drawings.” Their trapeze dresses were influenced by Twiggy, he adds.

Luckily he and Postgate were evidently both hoarders: the Museum of Childhood exhibition has all the original puppets, storyboards, sets and scripts. This includes The Clangers scripts, which were all written out and then “played” on the swanee whistle. In one script Major Clanger “says” of a door: “Sod it, the bloody thing’s stuck again.” A 1970s TV nerd would live for these details. But you sense that Firmin thinks the fascination with his work is all a bit odd. A mistake, really. “I think of myself more as a printmaker than all this television rubbish,” he says.

He is currently hand-printing hundreds of limited-edition Bagpuss prints on an ancient printing press in his not-at-all converted barn which is not-at-all warmed by a heater older than Bagpuss. The prints will be available to buy at the Museum of Childhood. Firmin is supposedly retired, but this is clearly the studio of an active, working artist.

‘I did the drawings and Joan worked out the knitting patterns from the drawings’: the original Clangers, now at the V&A. Photograph: Victoria & Albert Museum

The Firmins started married life in the early 1950s in a bomb-damaged flat in Battersea: “Two guineas a week with an outside loo and a bathtub in the kitchen.” Firmin was working as an art lecturer. It was on the door of this flat that Oliver Postgate, a stage manager for ITV, knocked. Someone had told him Firmin was a decent illustrator and could help him with some designs he needed for a new children’s programme.

“This gent came to the door who was working for the television. We didn’t have a TV set. The only TV I’d seen was when I was demobbed at Chatham and I saw a bit of Sunday Night at the Palladium. I thought it was rubbish.” But Postgate was offering six weeks’ work on a programme called Alexander, King of the Mice. It was £30 a week. Firmin was earning £15 a week. So that was that.

Their first films were crude, with all the “motion” done using magnets and mirrors. “Most television was broadcast live at the time and if you saw the hand popping up beneath the puppet there was nothing anyone could do.” As Joan says, they didn’t watch the results anyway. “We didn’t buy a telly for ages. I met a lady at the park and had to ask her if I could come round and watch hers.” Alexander was a hit in 1959 (on a budget of £175 an episode) and led to Ivor the Engine, Noggin the Nog and Pingwings in the early 1960s, and The Clangers and Bagpuss in the 1970s. After a 43-year hiatus, The Clangers returned to CBeebies in 2015 and won a Bafta for best pre-school animation. Firmin gave it his blessing and is part of the team who create it, saying: “It has more detail and much more subtle animation than the earlier series.”

It’s obviously gratifying to get some recognition. “When we were making these children’s programmes we were treated [by the television world] like the poor relations,” says Firmin. “It was almost like a punishment for the directors.” Any staying power of his creations is down to simplicity, he says. “In fact they were so simple that children could almost see how they were made,” says Firmin. “Nick Park of Aardman Animations told me that Ivor the Engine was a huge influence on him because he could see how it was done and thought: ‘I could do that.’ Now it just looks like magic. You can’t see how it is done.”

Inside story: Firmin’s studio desk, with prints, wire and gaffer tape – the tricks of his trade. Photograph: Pal Hansen/The Observer

Firmin has since acquired a reputation as a pioneer of environmentally friendly art. “I didn’t think of it as recycling at the time. We were just under-funded. And I was mean, too. So I’d just look at what I had lying around and think: ‘That would do for The Clangers.’” Their ideas often emerged after a prompt from a producer. (Firmin portrays them as saying: “What have you got for us now, dear?”) “The Clangers were created when the BBC asked for an idea about space. It was before they showed the footage of man landing on the moon,” he tells me. The night it was shown they stayed up and watched the moon landing anxiously. They were worried that if something went wrong their TV series would be cancelled. The Clangers made its debut in November 1969, four months after the moon landing. There were 78 episodes (and three specials) and it ran until 1974.

The inspiration for Bagpuss came from a Czech book which featured “a cat with live thoughts”. “Madeleine [the doll in the series] was a rag doll Joan used for the girls as a nightie case,” Firmin explains. Professor Yaffle – “the font of all knowledge” – was a hasty replacement for “Professor Bogwood”, a wooden man with a top hat and umbrella. “The BBC hated it. They said, ‘Stick to animals and birds.’ So we did a woodpecker instead.”

Firmin and Postgate seem to have had an unusually harmonious relationship. They lived a few miles apart for almost five decades and worked in adjoining studios. Firmin puts it very simply: “When two people work together, you complement each other. We felt our future was together. He did the writing and I did the making. I could draw the things that he imagined. It was the perfect partnership, really. I didn’t interfere with the stories.”

For many years Postgate was the more prominent of the two. It doesn’t seem to rankle. “Oh, I was happy to be his assistant,” says Firmin. “The writer gets the main plaudits. But we always made it clear that it was a combined effort.” At one time Firmin seems to have said to himself that he “didn’t have the education” to write his own stories. Similarly, Postgate was envious of his partner’s artistic talents. Later on, though, they both evolved. “Eventually I wrote books and he did illustrations.” He adds, kindly, “He suddenly found he was an artist after all.”

The Clangers, Bagpuss & Co is on from 19 March to 9 October at the V&A Museum of Childhood, Cambridge Heath Road, London E2. Free entry (vam.ac.uk/moc/home)