When radio presenter Roy Plomley came up with the idea for Radio 4's Desert Island Discs on a cold November night in 1941, on his way to bed and already in his pyjamas, he envisaged a series of six programmes. They began on 27 January the following year, 70 years ago this weekend. The show, which bases interviews with public figures around eight musical choices, a book and a luxury, is now the world's longest-running factual radio programme.

Unlike The Archers, which slipped up by over-hyping its 60th anniversary edition last year and killing off a popular character, Desert Island Discs is sticking to what it knows for its 70th, welcoming Sir David Attenborough back for a fourth appearance. Only Arthur Askey has matched that and Attenborough is a fitting choice for the 70th anniversary: a national treasure with a career of impressive longevity, just like the show itself.

Its appeal lies largely in a deceptively simple format – in talking about a fantasy island and their music selections, guests relax and reveal aspects of themselves – and a seemingly unchanging quality, underlined by the fact that it has only had four main presenters.

Plomley quizzed castaways for 43 years until his death in 1985, lunching before the recordings with the guest at his club, the Garrick (another club was used for female guests), and dealing with any anomalies in record choices, he explained in a Radio 4 documentary made for the 50th anniversary , by taking castaways across the road to the pub for "a couple of large gins".

The format and tone has quietly evolved over the years. The original didn't feature books or luxury items, with these added in 1951. Actor Sally Ann Howes chose garlic as the first luxury, a more prosaic choice than many that would follow: a blow-up doll (Oliver Reed), Michael Palin, stuffed (John Cleese), solar-powered vibrator (Cornelia Parker), mirror (Simon Cowell, Graham Norton), navel brush (Frank Muir), suicide pill (Peter Nichols, Stephen Fry, Lynn Barber), and happiness. The latter, requested by Brigitte Bardot, caused Plomley momentary consternation; it sounded as if she was asking for "a penis".

When Michael Parkinson took over from Plomley, he changed the interview so that guests heard their music choices rather than having them edited in. Plomley's widow, Diana, was said to find his style too slick, and Parkinson only hosted the show for two years.

She was even more scathing about Sue Lawley's 18-year tenure, claiming that the presenter had "an extraordinary obsession with other people's sex lives". This followed Lawley's 1996 interview with the then unmarried shadow chancellor, Gordon Brown, in which she said: "People want to know whether you're gay or whether there's some flaw in your personality that you haven't made a relationship?"

Lawley was host for the most controversial guest, Lady Diana Mosley in 1989, in which Mosley described Hitler as "fascinating" and challenged Lawley's assertion that the Nazis had murdered six million Jews. "Oh no, I don't think it was that many," Mosley replied. There was a long, icy pause. "Tell us about your fifth record, Lady Mosley."

Since taking over as host in 2006, Kirsty Young's time on the programme has been largely controversy-free, apart from some grumblings that Gok Wan was too populist a choice of guest. However, Young is widely credited with reinvigorating the programme, with her warm yet searching questions producing especially captivating editions with Kathy Burke, Mark Gatiss, Betty Driver and Morrissey. The latter's encounter was voted second best broadcast interview of all time in a Radio Times poll last year, pipped by David Frost interviewing Richard Nixon.

The programme's core strength is that it's a gentle listen, but one in which guests give us a strong sense of what they're really like. This might be through their musical selections – soprano Elisabeth Schwarzkopf famously chose seven of her own performances –or how they weave their life story around them.

The tone may be pretty relaxed, but like the programme's theme tune, it's not quite what it seems. Eric Coates composed By the Sleepy Lagoon in 1930, and it's now synonymous with being transported to a tropical island. In fact, he wrote the music while looking out over Bognor Regis. Similarly, Young will be welcoming and respectful to Attenborough on Sunday, but no pushover. Expect a question or two about those polar bear cubs featured on Frozen Planet that were filmed in a German zoo.