Sir Terence Conran: No designs on taking it easy

His furniture has inspired generations. Now 80 next month, he tells Sophie Morris why his new range for M&S will take over from where Habitat left off

Sir Terence Conran has a couple of M&S suits hanging in his wardrobe which he hasn't yet tried on. His wife picked them up for him because they were, he tells me, "quite remarkable value". If you don't think of Conran as a man with high-street tastes, you're right – he usually has his suits made by a tailor who works with his eldest son Jasper, the fashion designer. "You could buy 300 M&S suits for the price of one my others," he jokes.

But of course Conran should dress in the best threads Savile Row can provide. He has built up a quite remarkable fortune over a long career in the design, restaurant and retail industries, where style, form and function, as with a decent suit, are all major players.

Next month he will celebrate his 80th birthday with a party and fireworks at his Berkshire home, but there are no plans to wind down.

Instead he is preparing to unveil perhaps his biggest job yet, a major new home furnishings range for Marks & Spencer, while London's Design Museum is putting together a Conran retrospective.

"Twenty-one million people go through M&S every week," he says. "That's almost the entire population." He is staking his design credentials against the same folk who design the new suits, so it's to be hoped he likes them.

Many people associate Conran with high design and rarefied living. For a time his restaurants ruled the London dining scene: Bibendum, Le Pont de la Tour, Quaglino's (10 years after opening, 25,000 of its Conran-designed ashtrays had been pinched), and latterly Lutyens, Boundary and Albion. His London store, The Conran Shop, sells expensive modern classics. "I have put an awful lot of effort into it," he says, "but I am aware it only reaches a small segment of the population, who are from London and reasonably wealthy."

This had never been his intention. As he has said many times, Conran always wanted decent, functional design to be available to as many people as possible. It's an exaggeration to say that M&S reaches the entire population – its aspirational status was revealed on The X Factor last week when a contestant said it would be his first stop once he was a rich pop star – but its more than 700 stores nationwide do serve the millions of Brits who can afford to shop there. This new collection gives Conran the biggest potential customer base of his career. That's quite a birthday present.

The initial capsule collection of distinctly Conran pieces will arrive in selected stores this month. He and his team had just 10 days to finish the design process once the deal had been done with M&S chief executive Marc Bolland, but at an early viewing it doesn't look as if there have been many compromises.

There are armchairs with the signature Conran form: lazy, easy, but still very much structured, and a collection of shelving and tables, the Brindley Collection, made from oak veneer boxes strapped together in various asymmetrical constructions. There is, of course, a modular sofa incorporating a corner unit, and then Conran's personal favourite, the Marlowe armchair, which combines the look and comfort of a huge duvet crying out to be curled up in, with a smart, upholstered chair. "It is made from four cushions," explains Conran. "You can take the legs off and then you have a sort of low Japanese-style dining chair."

In a way it is surprising that M&S and Conran have not paired up before. He has done some designs for John Lewis, and for all his pioneering work at the tipping point of great British design and living, his driving force, as he has said again and again, has been to democratise design.

His first step in this direction was to open Habitat in Chelsea in 1964. "There was absolutely nothing back then. Nothing at all. Now the high street is not lacking, and there are many small shops doing excellent and affordable work as well. Ikea has a fantastic range, but it suffers because people don't have a good time when they visit."

Habitat introduced many firsts onto Britain's home furnishings landscape. Conran is very fond of the country's first flatpack range which he designed for the store, Summa, which will be celebrated in the Sir Terence Conran – The Way We Live Now exhibition at The Design Museum from 16 November.

Habitat introduced items into British kitchens which became essential as our culinary tastes diversified, such as airtight jars for dried pasta. The store was an international success, and although Conran has not been involved with it for years, he reacted to the news earlier this year of its closure, apart from the three London stores, "with great sadness".

"It has had very poor management and its buying directing has not been very good," he says. "It didn't have a dedicated designer working on its collections."

If you have never been to one of Conran's shops, you might well look at the M&S collection and recognise what you see. He has influenced several generations of designers and is much copied, which he finds flattering, although he doesn't like the sort of copies being done in China – direct copies of classic items of furniture. "You can buy a new lounge chair for tuppence ha'penny, but it's not well made, and if you come to sell it, you won't get anything for it."

Conran loves great design, such as an Eames chair – "full of humour and wit" – but is not a champion of grand design. "I'm a bit disturbed at the moment by this thing that Ron Arad has been responsible for, art furniture. Do you know what I mean by that? Where pieces are statements and cost hundreds of thousands of pounds. I like things which are plain, simple and useful."

Can Conran, via M&S, reach the people who have an Eames in their sights without the few thousand necessary pounds kicking around to acquire one? The collection includes a wide selection of ceramics and glassware, a striking Kilim rug in purple or green from £149 and an oak dining table for £699. Yet several of the armchairs are £999. He's said his target market is a teacher. Can a teacher afford a £1,000 armchair? "I think so, yes. Because of the quality of it." We'll see.

From the beginning, Conran said that his collaboration with Marks & Spencer had to be an ongoing arrangement. "I said it should not be a one-off collection, because in order for it to have any success, it needs to run on into the future." It's a great way to pad out one's pension, but it also gives Conran the scope to pick up where Habitat has left off. Where money-conscious consumers might be cutting down on shopping trips and have avoided Habitat because, say, new garden furniture is not essential, they still visit M&S for their knickers and a lunchtime sandwich. And as Conran will also design pieces to appear in the food and lingerie departments once the full furniture collection of several hundred pieces comes out next spring, they might find themselves admiring his work while deliberating between egg and cress and roast beef of a lunch hour.