Last Night's TV - Imagine, BBC1; Pompeii: Life and Death in a Roman Town, BBC2

Faith, hope and chariots

It's like wading through sick," said Lee Lyford disconsolately, halfway through Imagine's film about the making of a theatrical adaptation of the sword-and-sandals epic Ben-Hur. Lyford was the director, one of just a handful of professionals involved in the production, and what was making him feel queasy was the unreliability of some members of his cast, a third of whom had failed to turn up for a rehearsal. At which point, Radio 4 regulars will have heard a very familiar voice commenting on the proceedings. "Is there any point?" it asked plaintively. "The entire project seems to be disintegrating anyway."

The voice was that of Marjorie Antrobus from The Archers, or rather of Margot Boyd, who played her, and was so determined to share her love of theatre with the people of Bath that she left a large chunk of money in her will to fund a drama project, the one proviso being that all those on stage should be amateurs. The director, Fran Landsman, or some diligent researcher, had trawled through The Archers archives so that Boyd could comment on the proceedings from beyond the grave – a nice touch which, apart from that one little dip in morale, mostly delivered encouragement and praise.

As did Lyford himself, of course, working on a project that offered some advantages (there was no shortage of parts), but also some signal challenges. How exactly were they going to stage a sea battle in a trireme, or the film's famous chariot race? Lyford candidly confessed that he didn't have a clue, but seemed confident that they would get there somehow. The solution to one of these conundrums helpfully mopped up some of the overspill of theatrical ambition, which became clear at the early auditions. Those who missed out on the speaking parts got the chance to play a small section of the Mediterranean – a rehearsal process that provided one of the funnier sections of Landsman's film – as Lyford encouraged his cast to really immerse themselves in the full sloshy liquidity of their role. "Really remember this quality," he told them, as they swayed gently like strands of kelp in an ebb tide, "because you have to be able to click into this."

There was, unsurprisingly, quite a bit of stage fright. One novice, Poppy, decided to pose nude for a life class first as a way of desensitising herself to public exposure, which struck you as being a bit like amputating your hand because you've got a splinter stuck in your finger, but seemed to work anyway. Another actor, Caroline, treated the whole enterprise as a kind of life-therapy. "I'd totally lost the sense of myself," she said about the effect of full-time motherhood, but she appeared to have found it again by pretending to be someone else entirely. And, of course, in the end the performance was a triumph, with the chariot race being mimed on the cramped stage of the Theatre Royal to the accompaniment of a Grand National style commentary on the publicaddress system. "I'd say he's cracked it," said Alan Yentob, with reference to Lyford's biggest challenge. I'd say Yentob was being quite kind, frankly, but there was something about the enterprise – the eagerness, the pleasure and the sense of enlargement it gave – that made it virtually impossible to be anything else. Margot Boyd got her money's worth.

The Roman members of the cast traipsed round the Roman baths at one point, as part of their research, picking up on their availability to citizens high and low but missing the fact that there was no plughole. Mary Beard pointed this out in Pompeii: Life and Death in a Roman Town, also spelling out the corollary, which was that Roman bath water got filthier and filthier the more people used it. A doctor at the time warned anyone with an open sore that it was best to give the baths a miss unless you wanted to develop gangrene. Beard claimed she was on a mission to "bust a few myths" here, and she drew on the relatively recent discovery of 34 bodies in a Pompeian cellar to fill out what we already know from the ruins of the Roman city. But the myths, when you got to them, didn't strike you as being very convincing. How many people really believe that Roman society consisted of lark's-tongue-guzzling aristos and malnourished slaves, with nothing in between – one of the "received opinions", which Beard overturned?

Fortunately, she's quite engaging anyway – the sort of classicist who says "willy" rather than "phallus", and isn't too stuffy to confess to a sense of thrill when she tries on a gold Roman bracelet. In any case, it's virtually impossible to make a dull film about Pompeii, in part because of the energies of the city's Tweeters, who – lacking smart phones – had to inscribe their updates on the nearest bit of masonry. "I was here and had a good shag", one unknown Pompeian had scratched into the wall of the town's brothel, though I suppose that could be taken as a posted user's comment, rather than a Tweet. And in one of the town's jakes someone called Apollinaris, doctor to the Emperor Titus, had whiled away a bit of time engraving his name and the phrase "hic cacavit bene" or "had a good shit here". The eruption of Vesuvius, not very long afterwards, has preserved for nearly 2,000 years the evidence that the desire to share your bowel movements with the world is not an eccentricity unique to our own times.