This genuinely painful scene - in which childhood hopes for what Christmas might deliver bumped hard against adult failings - made you brace yourself for something remedial, something sour and harsh, as an emetic for the sugar overdose which Christmas television conventionally delivers. What followed, though, was far more hopeful in tone, a tale of rescue and redemption.
Vanessa, the oldest child of four, decides to take matters in hand after her mother collapses in a sozzled heap. With Daddy staying at his girlfriend's flat and the nanny off to Denmark for the holidays, the way is clear for a spot of protective custody; so the children lock their mother in the basement sauna and put her on a diet of compulsory cold turkey.
Despite that opening, Mothertime couldn't exactly be described as gritty in its realism - the sauna included the somewhat unusual design feature of a very large letterbox, to get round the problem of how the children feed their prisoner, and the plot was aided by Vanessa's handy ability to do a perfect imitation of her mother's voice, good enough to fool her ex-husband and other curious grown-ups.
But even though it poured sawdust into the gearbox to mask unsettling rattles, Mothertime conveyed some real truths - about childhood disillusionment and parental failure. The mitigated happy ending - mother restored to loving sobriety but father dispossessed of his daughter's unquestioning adoration - left you feeling hopeful but not entirely convinced.
Matthew Jacobs's deft direction of his own adaptation of Gillian White's novel (he particularly enjoyed the long bout of delirium tremens) was also assisted by an excellent performance from Kate Maberley as Vanessa, determined and resentful and vulnerable by turns.
One of the other one-off dramas shown over the Christmas week also ended with a rising inflection that seemed to owe more to seasonal goodwill than to cold-eyed realism. Guy Jenkin's Mr White Goes to Westminster (Tuesday, Channel 4) concluded with his hero vowing to battle on against corruption, cynicism and circulation-boosting lies. The plot and characters for Jenkin's satire had been supplied by life, but only as far as the first ad break - after that he had to work out what to do with his Martin Bell figure - an ex-war correspondent who stands as an independent against a sleaze- stained Tory candidate.
His solution was a good one, with the MP winning the ballot for Private Members' Bills and attempting to push through legislation which would compel newspapers to offer redress if they published lies about ordinary members of the public. What followed was partly a tutorial on how a sharp- edged Bill can be polished to innocuous smoothness by its passage through the party machine, partly an exploration of how private honour and public probity might easily twist themselves into an unloosable knot. (White's bill is secretly supported by his former lover, an ambitious Labour backbencher - he can't reveal the source of his funding to the rapacious hacks without dishing her career.)
Since he had constructed this tangle with some care, it was a bit surprising that Jenkin should cut it apart so casually, with all the principal characters suddenly displaying a spotless and self-sacrificing nobility of character. Perhaps he wanted a bit of Capra optimism to finish with - but you couldn't help feeling that he was going against form as he did so - that the unruly contempt that supplied some of the best jokes here had been temporarily silenced just because it was Christmas.