Well, who'd have thought it of Hattie Jacques. According to BBC4's latest showbiz biopic Hattie, the celebrated comedienne, played by Ruth Jones, conducted quite a carry on of her own back in the sixties. Married to the actor John Le Mesurier, Jacques took a lover ten years her junior and proceeded to move him into the family home as their lodger. Upon discovering the infidelity, Le Mesurier declined the invitation to move out, choosing instead to swap his bed for that of the boyfriend and become cuckold/lodger in his own house. A bizarre compromise that satisfied no-one.

As always with BBC4 biopics, the period was beautifully recreated and the performances top notch, but I never came close to comprehending the characters' behaviour. Nor did I like any of them, although Jones' worked hard to show Jacques charming side. Perhaps Hattie can best be understood and appreciated as a triangular love story fuelled by selfishness, shallowness and cowardice. Not a bundle of laughs, it must be said, but gripping in its own warped way.

A revealing rifle through Hattie's knicker drawer

This wasn't just a glimpse behind closed doors, it was a thorough rifle through underwear drawers and dirty laundry. And for Jacques, events were always arcing towards that hotel room at the start. It was beautifully shot and acted. I put on one of the Saw movies afterwards for some light relief.

Last Night's TV: Hattie/BBC4

Ruth Jones played Jacques, a piece of casting that on paper may have seemed to make sense physically, but didn't entirely in practice.

Hattie review

I always think a TV biopic has done its job when you come away wanting to know more about the people involved.

It takes a special kind of love to move into the lodger's room in the attic while your wife makes hay with her fancy man in the master bedroom. But that was the peculiar domestic set-up at the conflicted heart of Hattie, the true - yes, true - story of Carry On comedy legend Hattie Jacques.

Ruth Jones certainly looked the part of Jacques, all twinkly eyes and comfortable cleavage, her sunny smile masking the frustration of a career cul-de-sac. 'I know my casting; I'm the frigid fat girl,' she complained, acknowledging her role as the nation's favourite chubby, a 1960s Dawn French, if you like.

But though she gave a good impression of warmth, Jones's Hattie strayed a touch too close to heartless bitch for this remarkable story to fully convince. The heart of the tale belonged to wronged husband John Le Mesurier, played by Robert Bathurst with just the right measure of unqualified love and ruffled dignity. 'He's too vague to be unhappy,' claimed Hattie, granting herself licence to cheat, but Bathurst's nuanced performance turned Le Mesurier's vagueness into a self-protective shield.

As a period piece Hattie worked superbly, its glimpses of Carry On film sets, with Marcia Warren scene-stealing as an embittered bit-parter ('I'm sick of this batty old lady s***') a diverting treat. But we didn't get enough of the self-esteem issues that bedevilled Jacques and led her to jeopardise a happy marriage by falling for a devilishly handsome wheeler dealer who made her squeal between the sheets. She fell rather too easily.

Desperate Romantic Aiden Turner certainly looked the part, all moody scowl and hairy chest, but his gor-blimey accent was comedy working class. 'I'm not a bit of rough!' he exploded but that's exactly how he came across, fine for a lusty leg-over but hardly a prospective long-term partner. Which was why Hattie kept her husband in the house to talk to, during the intervals between the sex olympics.

As I said, peculiar. It fell apart when Le Mesurier met a new love, though everyone remained remarkably civilised, and Hattie's bit of rough ultimately left her. It was all quietly sad and a noble attempt to tell a tricky tale. But I never quite fell for it.

If a biopic of Britain's favourite "silly, frigid, fat girl", Hattie Jacques, sounds a lark, then be warned: this is a bittersweet drama that focuses on the actor's relationship with a younger lover. It's an affair that ultimately destroys her marriage to Dad's Army actor John Le Mesurier - who was also cuckolded in a similar BBC4 biopic, Hancock And Joan - as Jacques, hopelessly in lust, moves her lover into her marital home as a lodger. Ruth Jones, deftly showing Jacques as both selfish and capable of self-deprecating charm, heads an impressive cast.

Hattie Jacques: How we filmed her bittersweet tale

We all felt it was time to look at a woman in comedy and it would be interesting to portray a comic whose life was more colourful off screen than her roles ever suggested.

Hattie Jacques's career as a comic actress saw her appear in 14 Carry On films and build a long-term working partnership and friendship with Eric Sykes. But this focuses on her marriage to Dad's Army star John Le Mesurier, which was interrupted when she had an affair with a cabbie and moved him into the marital bed, with Le Mesurier moving into the attic room upstairs. That Jacques and Le Mesurier remained on good terms is testament to Jacques' magnetic, scrumptious warmth, which actress Ruth Jones captures here beautifully.

Ooh, matron! The real-life bed-hopping antics of Hattie Jacques were a far cry from the sex-starved battle-axe she played in the Carry On films.

Gavin and Stacey's Ruth Jones pours herself into a series of shiny sixties frocks and some sexy corsets for this handsome one-off biopic. Meanwhile Aidan Turner - of Being Human and Desperate Romantics fame - is transformed after a run-in with the hair-straighteners into her toyboy, bit of rough John Schofield.

When Hattie divorced Dad's Army star
John Le Mesurier (played by a very well-cast Robert Bathurst) in 1965, it was reported that he had cheated on her.

In fact, the mild-mannered Le Mesurier was the innocent party while Hattie had been living the best of both worlds - moving her husband upstairs to the attic, and her lover - a cockney car-salesman - into her marital bed.

It doesn't exactly show Hattie in a favourable light. How could she do it to the lovely Le Mesurier? As she explains to a girlfriend while Schofield hunks about the garden, bare-chested in shorts: "Ooh, look. Him! With me!"

Ruth Jones is mesmerising as Hattie Jacques, the beloved comic actor and Carry On star, who became part of a domestic ménage with her adored husband John Le Mesurier and a sexy younger man, John Schofield. The story is irresistible: Schofield (played by Being Human's Aidan Turner) is a second-hand car dealer who meets Hattie after a charity event while she's filming Carry On Cabbie and the two are quickly in the grip of an electrifying sexual passion. Bizarrely, even incredibly, Schofield moves into the Le Mesurier family home and the marital bed, with John Le Mesurier banished to the lodger's room in the attic. Yet Stephen Russell's script judges no one as it reveals a marriage that, in its own strange way, was rock-solid: Hattie and Le Mesurier shared a lifelong devotion after their divorce. Ever the gentleman, Le Mesurier (Robert Bathurst) 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.