There is a terrific warmth and tenderness to Kenneth Branagh’s elegiac, autobiographical movie about the Belfast of his childhood: spryly written, beautifully acted and shot in a lustrous monochrome, with set pieces, madeleines and epiphanies that feel like a more emollient version of Terence Davies. Some may feel that the film is sentimental or that it does not sufficiently conform to the template of political anger and despair considered appropriate for dramas about Northern Ireland and the Troubles. And yes, there is certainly a spoonful of sugar (or two) in the mix, with some mandatory Van Morrison on the soundtrack. There’s a key climactic scene about how you disarm a gunman in the middle of a riot if you have no gun yourself, which has to be charitably indulged.

But this film has such emotional generosity and wit and it tackles a dilemma of the times not often understood: when, and if, to pack up and leave Belfast? Is it an understandable matter of survival or an abandonment of your beloved home town to the extremists? (Full disclosure: my own dad left Belfast for England, though well before the era of this film.)

It is 1969 and Jamie Dornan plays a man who lives in north Belfast, a largely Protestant district but still with some Catholic families. He is an easygoing charmer, away in England a fair bit during the week, doing skilled carpentry work and harassed with the need to pay off a tax bill.

When his long-suffering wife (Caitríona Balfe) writes to the Inland Revenue asking for confirmation that his debt is finally paid off, it prompts the authorities to look further into his murky affairs and decide he owes another £500. This is such a horribly unglamorous, un-cinematic moment that it surely has to be taken from real life.

The family includes two boys, the older Will (Lewis McAskie) and younger Buddy, played by newcomer Jude Hill, whose stunned, wide-eyed incomprehension sets the tone. The grandparents live with them under the same roof and are played with beguiling sweetness by Ciarán Hinds and Judi Dench (the latter pinches every scene by deflating the menfolk with wisecracking remarks from behind her copy of the People’s Friend).

Violence explodes when unionist hardmen burn the Catholics out of their homes and set up barricades to protect their new fiefdom against republican retaliation – a gangsterism that requires payments from local families, enforced by tough guy Billy Clanton (Colin Morgan), accepted more or less pragmatically by local man Frankie West (a great cameo from Michael Maloney) but resented by Dornan’s character. He starts showing his wife and kids assisted-emigrant brochures for Vancouver and Sydney: places beyond the reach of the terrorists and the taxman but so alien they might as well feature on Star Trek, which the boys watch on TV every week. And poor Buddy just has to carry on with his life, which involves much unrequited pining for a girl in his class.

The film moves with an easy swing from home to street to schoolroom to pub and back home, and it’s perhaps fullest and richest when nothing specifically tragic or Troubles-related is happening. I loved the scene in which Buddy is schooled on what to say if a stranger demands to know if he is Protestant or Catholic: does he lie or double-bluff with the truth? (I was reminded of the Dave Allen routine about what happens if you try sitting on the fence and claiming you’re Jewish – the hard man replies: “Are you a Protestant Jew or a Catholic Jew?”)

The family get some escapism at the movies: Raquel Welch in her furry bikini in One Million Years BC, the flying car going over the cliff in Chitty Chitty Bang Bang, and High Noon on TV. There’s a trip to the theatre to see A Christmas Carol; the late John Sessions gives his final performance as the Belfast stage actor Joseph Tomelty playing Marley’s ghost. But inevitably Buddy gets drawn into some scrapes: nicking a bar of Turkish delight and then getting involved in looting a box of washing powder from a riot-hit supermarket.

It’s not quite right to say that there’s a streak of innocence in the nightmare of this film, but certainly a streak of normality and even banality, which assumes its own surreal tone. Love letters to the past are always addressed to an illusion, yet this is such a seductive piece of myth-making from Branagh.

'Belfast' is released on 21 January in cinemas.