The Weekend's Television: Small Island, Sun, BBC1</br> Being Alan Bennett, Sat, BBC2

Small Island opened with an illusion that we knew – within just three or four words – was doomed to be shattered. "Put the word 'mother' in front of 'country'," said a male voice, "and you think of somewhere safe, where your potential will be nurtured and your faults excused."

Why are we so certain – so soon – that what follows will strip away those naive expectations? Because we're cynical by nature, I suppose, and have learnt to be wary of patriotic abstractions. But also because we can see that the possessor of these dreams, Hortense, is black, and most of us will know that the mother's welcome was dubious, to say the least. Small Island began in chilly light, with Hortense alone in a Tilbury arrivals hall, and the story tantalised us less with what would happen next than in how she came by her hopes in the first place.

There's a lot that's great about the adaptation of Andrea Levy's book. It looks wonderful – the Caribbean scenes sun-faded like an old photograph of the colonial past and the London sections dark with smog and nicotine stains. There are moments – the gas light flickering in a pre-war interior – when you can barely make out that it's still in colour. It's also well cast in its twinned lead roles, with Naomie Harris pertly self-regarding as Hortense, whose anglophilia is so tragically at odds with the drab reality, and Ruth Wilson excellent as Queenie, also yearning for an enlarged horizon, also prepared to marry without love to get it, but from a Yorkshire pig farm rather than the cane plantations of Jamaica. A world divides these two – Hortense survives a genuine hurricane while for Queenie it's just a tricky word in an elocution lesson – but the world also contrives to bring them together, in the run-down Brixton boarding house in which Hortense's husband finds lodgings.

What doesn't work quite as well is the voiceover narration, which often gives the thing an overblown, sententious tone. Rather than playing down the melodrama of the plotting – in which raging storms and bombing raids accompany the crises in the characters' lives – it heightens it, with words that hover dangerously close to truism ("How people's lives entwine together is one of life's mysteries," intoned the parsonical voice, "but they say God works in mysterious ways.") It can also be unintentionally comic. As Queenie and Michael writhed naked on the bed, seized by passion, we were suddenly startled by a pontifical third party, reading a sermon over their spliced bodies. "There are two kinds of love," said the voice gravely. "One is solid and enduring like the ground beneath your feet. The other is a hurricane, fierce and powerful." Even as the characters are bowled towards Queenie's first orgasm, the voiceover is butting in to turn them into representative types. Having said which, when it shuts up, the drama is often beautifully underplayed, and its account of what for many people was a stark disenchantment still painfully tender to the touch.

In Being Alan Bennett, the eponymous subject appeared to suggest that disillusionment had never been a problem for him – or at least that it often worked in reverse. "I've always had a sense that the best is over really," Bennett confessed, "even when I was 16." Every now and then, though, life would give him a nice surprise and prove that there was still more to come. This profile of him will have stirred déjà vu in anyone who saw The South Bank Show's portrait a few years ago, which also played on the distinction between actually writing and being a writer for the camera. But he does both so well it was a pleasure to watch anyway.