Playwright Martin McDonagh’s story of two Dublin hitmen, holed up in Bruges after a killing has been botched back home, achieves the difficult feat of being both funny and moving, often at the same time. It’s not a very good title for an excellent little film that’s beautifully acted, very well shot and written with real flair by its director.

Ken (Brendan Gleeson) is the older of the two, at least capable of appreciating the best preserved medieval town in Europe as the pair await orders from Harry (Ralph Fiennes) in Dublin. Ken would like to get out of the game and his face is creased with both worry and wonder as he wanders the town.

Ray (Colin Farrell) is the boyo who couldn’t care less about the various tourist attractions but meets a girl at a local film shoot (Clemence Poesy) and finds some sort of reason to stay. Unfortunately, just as he is about to bed her, her boyfriend arrives with a gun and, since he is a practised fighter, Ray manages to shoot him in the eye with a blank.

He also meets a little man on the set (the excellent Jordan Prentice, at last given some decent lines) who wants to be called a dwarf rather than a midget and gets a karate chop from Ray when he proves a bit of a racist, too.

That’s two enemies he’s made, but the worst one is Harry, who arrives furious from Dublin after a hideous row with his wife, and is determined to punish him.

Harry wants Ray done in as a matter of honour. His last job was to shoot a priest at the confessional, which he did well enough, but he also succeeded in killing a small boy about to confess his sins. Harry has told Ken to shoot Ray, but the older man has baulked at the assignment, feeling Ray still has something worthwhile left in him.

Even killers have a threshold beyond which they are not prepared to go — but the main point is that these three men are locked into their profession of violence and, however much they struggle, can’t easily get out of it.

The swear-infested dialogue, and the bloody nature of the denouement, has given In Bruges its 18 certificate. But it is an exception to the general rule of such movies in that its dialogue and attention to character allow the emotions to sway this way and that through near-farce to tragedy.

All this might have been for nought but for the performances. We know Glee-son is an exceptional actor from John Boorman’s The General. We also know that Fiennes, given something to bite on, can achieve small miracles. But we rarely see Farrell so good, using his charm well but not too much and also suggesting a guilt-ridden man who has no idea what to make of his life.

This is one of the best surprises in London at the moment, made by a writer-director who really knows what he is up to.