Watching Burton and Taylor (BBC4, Monday) I felt a bit like I do when I go to the theatre — or, more often, when friends have kindly taken me to the theatre. ‘Are you enjoying it?’ someone will ask. ‘Oh, yes. Very much,’ I’ll lie. For the truth is, no matter how well done it all is, I’d still so much rather be doing other things. Catching up with the latest episode of the infinitely more gripping The Returned (Channel 4, Sunday), for example.

At the end I found myself wondering ‘Why?’ Not just ‘Why didn’t I switch off earlier?’ and ‘Why couldn’t I maybe have chosen to review that David Starkey series on royalty and music instead?’ but, most pertinently, ‘Why did they bother making this presumably quite expensive biopic?’ or ‘Why couldn’t it go on letting us enjoy Burton and Taylor as they were in our heads: as remote, unattainable fantasy figures defining a Seventies movie-star glamour the like of which we shall never see again?’

Consider, for example, all the outfits we saw Elizabeth Taylor (Helena Bonham Carter) and Richard Burton (Dominic West) wearing. We’ll have recognised many of them from the photos. Taylor in that famous black and white geometric patterned dress; Burton with his polo necks and his mink coats. But seeing Bonham Carter and West inhabiting them on the small screen didn’t make you go: ‘Why, it’s as if Burton and Taylor were standing there before us now.’ Instead, it just drew your attention to how not like Burton and Taylor they were.

Which is a shame because they had a good stab at it, a really good stab. West couldn’t quite capture the richness and resonance of Burton’s extraordinary voice (which the script plausibly had him describe dismissively as the acting equivalent of a ‘really big cock’) but gave him a nice, subliminal Welsh lilt, which passed. Bonham Carter displayed superb comic timing — as, for example, during the first read-through of Private Lives where she admits she hasn’t actually read the play yet — and captured almost perfectly Taylor’s maddening capriciousness and ruined magnificence. But — a problem with West, too — she didn’t look quite enough like her subject ever to allow you to forget that you were watching a bravura impersonation rather than the real thing.

So again: what was the point of the exercise? To show us that incredibly famous stars have feet of clay? Well, duh, I think most of us had twigged that one by now. (For example, I’ve never been able to enjoy Radiohead or REM quite as fervently since the day I met the weird and rather clammy Thom Yorke with the similarly remote and off-putting Michael Stipe.) And, anyway, I’m not sure there’s always something to be gained seeing our heroes in undress mode. The Queen, say: are we really all gagging for the warts-and-all exposé which finally shows her going to the loo or how she looks just after she’s got out of bed? I don’t think so.

It’s an especial problem with stars who are alcoholics and pill-poppers. Addiction is boring: boring to live with, boring and ugly and prurient to watch. As Bonham Carter and West recreated the wreckage of Taylor’s and Burton’s later career (when he was a year away from death; and she’d become a porky, sloppy, capricious late-middle-aged ham whose response to the rubberneckers who’d come to witness their car-crash New York production of Coward’s Private Lives was to mug at them vulgarly and shamelessly), I felt rather as you do when your dinner-party hosts suddenly break into a vicious public row. Couldn’t they have saved this grisliness till after we’d gone home?

I think what we had here was a classic example of — dread phrase! — a chamber piece. Everyone concerned must have thought it a frightfully clever idea to get a first-rate screenwriter, William Ivory, and a top-notch acting duo to create a sensitive, beautifully observed, poignant and lovingly crafted account of two legends captured with excruciating frankness in their sunset years.

But the result — as is so often the case with such exercises — presented much more to admire than to enjoy. Indeed, with its smallish cast and limited number of mostly indoor locations, it was positively made for theatre. Already, I can picture the rapt response of my theatregoing friends, raving about just how totally amazing Bonham Carter and West are in the title roles, and what an exhaustingly moving and harrowing and intimate chamber piece it is which leaves not a dry eye in the house.

Wish that’s the route they’d taken. Then Lloyd Evans would have had to review it, not me.