It's 100 years since the birth of John Le Mesurier, which is a good enough reason to take another look at the life of this adored actor.

There's nothing really new in It's All Been Rather Lovely (BBC2, 9pm) but it's nice to be reminded of his laid-back style and his extraordinary private life.

This is the man who briefly lost his wife, Hattie Jacques, to his best friend, comic legend Tony Hancock but who remained close to her.

He even took her back, without ever mentioning the split again.

Best remembered as Sgt Wilson, the Dad's Army star, who died in 1983, has a host of celebs queuing up to tell us what a thoroughly decent chap he was.

This documentary on Dad's Army. star John Le Mesurier contains only one clip when he is not performing - and that's from his appearance on This Is Your Life, honouring his then wife Hattie Jacques.

At the time she was having an affair with her driver John Schofield who she had installed in the family home, moving her husband into another room.

You'd never guess that from his demeanour here, so in a way this was very much another acting job.

His third wife Joan also appears here, talking candidly about her own doomed affair with his best friend Tony Hancock.

So you could say Le Mesurier was proof that nice guys finish last (where love is concerned anyway).

Nobody has a bad word to say here about the man whose perfect manners, playfulness and lack of ambition made him so universally adored.

Dad's Army co-writer Jimmy Perry explains how he was initially infuriated by his slightly negative, laid-back approach to the plum role of Sgt Wilson, who rather than barking orders asks, "Would you mind awfully falling in?" and wished he'd do more with it.

But it was precisely this distracted air that made the character so enduring and soon they were writing Wilson based on Le Mesurier himself.

It's fascinating to hear how he ­cultivated a unique aura of uselessness to the extent that he couldn't even make a cup of tea.

Or how he turned up for his first day in the Army with his dinner jacket, jazz records and golf clubs.

Whether or not that was all just an act too, John Le Mesurier was definitely one of a kind.

When John Le Mesurier's wife Joan left him for what turned out to be a brief and disastrous relationship with his best friend Tony Hancock, he became Joan's confidante. He'd comfort her in her unhappiest days with Hancock, telling her: "I love him too, I know exactly how it is, darling."

Everybody loved John Le Mesurier and the contributors here, including Joan, who left Hancock and returned to her husband (he never referred to her affair again) speak of him with unconditional adoration. Le Mesurier was peerless; that wonderful, urbane delivery and the crushed-velvet voice made him unforgettable as Sgt Wilson in Dad's Army.

To those who knew him best, he was charming, warm and delightful. Michael Palin worked with him on Jabberwocky and wonders fondly where Le Mesurier would be in 2012: "Playing a patient in a bed in Casualty?" Palin is a devotee of Le Mesurier's reassuring presence: "[when he appeared] I just felt comfortable. I knew he knew what to do."

Radio 4 commissions drama about Dad's Army

Dear Arthur, Love John, by West End playwright Roy Smiles, will chart the relationship between Dad's Army stars Arthur Lowe and John Le Mesurier and focus on the creation of the beloved TV series.

Radio Times review

The 36th best TV show of 2011 according to the Radio Times.

A superb example of BBC4's curious but rewarding obsession with mid-ranking, mid-20th Century entertainers, and the misery success brought them. Hattie Jacques, trapped by sexist typecasting and her supportive but inert husband John Le Mesurier, welcomes a sexy young lodger (Aidan Turner) into the family home and proceeds to have an affair with him. As Jacques, Ruth Jones captured the desperation of someone who knows, deep down, that she's destroying herself, but can't quite stop. Robert Bathurst was just as fine as Le Mesurier, who could see what Jacques was doing but couldn't quite rouse himself to prevent her. A sensational-on-paper story became sober, classy and sad.

On the Sunny Side of the Street plays in the background over an opening montage of quotes on the career of Hattie Jacques, from Sophie Tuckshop in ITMA on the radio to all those Carry On films. Barbara Windsor says she was "a national treasure", Eric Sykes (who played her brother in their long-running TV series) calls her "feisty", everyone says what a generous person she was. This isn't a totally sunny story, as anyone who saw that BBC docu-drama on her broken marriage to John Le Mesurier will recognise. But it is a kind one.

The Beeb's drama department has carved out a neat niche with its biopics of beloved British comedy stars: from Kenneth Williams and Tony Hancock to Frankie Howerd and Morecambe and Wise. This latest film, first shown on BBC Four in January, is a worthy addition. Gavin & Stacey's Ruth Jones stars in an acclaimed dramatisation of Carry On star Hattie Jacques's life. Though she played an austere matron on screen, Jacques's private life was actually rather racy. The story focuses on the early 1960s love triangle between Jacques, her chauffeur (Aidan Turner) and her husband, Dad's Army star John Le Mesurier (a heartbreaking turn from Cold Feet's Robert Bathurst) - whom she continued to love, even when she moved her toyboy into their bed. It's a bittersweet story, superbly acted, and followed by a repeat of Jacques's 1963 appearance on This Is Your Life.

If you missed this superior biographical drama when it was shown earlier this year, here's a good chance to catch up. Ruth Jones is mesmerising as Hattie Jacques, a beloved comic actor who became part of a domestic ménage with adored husband John Le Mesurier and sexy younger man John Schofield. The story is irresistible: Schofield (Being Human's Aidan Turner) meets Hattie after a charity event and the two are quickly in the grip of an electrifying sexual passion. Bizarrely, even incredibly, Schofield moves into the Le Mesurier home and the marital bed, with John banished to the attic. Yet Stephen Russell's script judges no one as it reveals a marriage that, in its own strange way, was rock-solid, with Hattie and John sharing a lifelong devotion, even after their divorce. Ever the gentleman, John takes the blame for the break-up. Hattie is a touching drama that, for once, doesn't perform a hatchet job on an adored British comedy figure.

In Hattie, Hattie Jacques (Ruth Jones) looked like she might be about to tell This Is Your Life host Eamonn Andrews to get stuffed, before composing herself and affecting modesty: "Oh Eamonn, they don't come much duller than me." Ha ha. What Andrews didn't know was that Jacques had just changed the man in the marital bed, despatching husband John Le Mesurier upstairs and summoning down their lodger.

No one knew this, This Is Your Life passed off without scandal, and in the divorce court, to protect Jacques, Le Mesurier pretended to have been the adulterer. "Thank you for ending our lovely marriage so beautifully," she said.

What a story! How civilised and quietly heroic and terribly British. Well, Le Mesurier was, anyway. The drama gave us nothing of Le Mesurier the actor and not very much of Jacques the actress.

Eric Sykes, in the run-up to BBC4's latest squint under the greasepaint of the great showbiz era, had complained about this.

But Hattie wasn't a sensationalist piece, just sad and moving and told in the usual Beeb 4 way with one classic car (the E-Type Jag driven by the fancy man, not his own), period lampshades, a fug of cigarette smoke, skinny ties, a dollop of casual sexism, a couple of old choons and, of course, a good script and some cracking acting.

Jones did that remarkable thing of making you forget all about her best-known role (Gavin and Somebody) but Robert Bathurst as Le Mesurier was even better, perfectly capturing his vagueness.

Swift production of the martini decanter solved most of his crises, although for having to tell his sons he was finally leaving he tried this sweetener: "I've got you both... pen knives."

I cheered when he remarried Jacques' friend Joan, completely forgetting that the latter's subsequent affair with Tony Hancock had been the subject of a previous Beeb 4 biopic. Pass the martini, old bean.

Has there ever been a more passive and diffident Englishman than John Le Mesurier? Last time he was dramatised was in a film about his best friend Tony Hancock, in which he stood politely by as Hancock ran off with Le Mesurier's third wife. Now he turns up in Hattie (BBC4) as Hattie Jacques's cuckolded husband (she was his second wife). Jacques - played in an exceptional performance by Ruth Jones - took in her used-car salesman lover as a lodger, and maintained a secret affair by the cunning means of slipping upstairs during the middle of the night. The scene in which she was finally discovered by Le Mesurier (a perfectly cast Robert Bathurst) in bed with her lover was a vision of tragicomic poignancy. He apologised for intruding and explained with consummate resignation that he was looking for his book - a James Bond novel. Seldom has the distance between reality and fantasy been so economically or movingly captured.