I'd been wanting to see this since reading about it in Ciaran Carson's The Star Factory, for purely personal interest reasons - the setting in Belfast, the connection with Doctor Who - but it really is a brilliant film in its own right. Even though you pretty much know what is going to happen right from the very beginning - terrorist bank raid goes wrong, the wounded leader staggers around the city pursued by friend and foe alike - the tension is maintained throughout. James Mason is superb as the central character, suffering angst and flashbacks, inspiring loyalty and love; and the whole thing is beautifully directed with great background music.
The approach to Belfast is ... peculiar. The film starts with a fantastic establishment shot from the air, coming in over the Lagan and zooming in on the Albert Clock and High Street (also the setting of the climax); but at one point we see the police inspecting a map of a completely fictional unnamed city on the edge of the fictional Fernagh Lough. However the trams in this city clearly go up the Falls Road! And while most of the adult actors seem to have southern Irish accents (basically because they were recruited from the Abbey Theatre in Dublin) the extras are definitely from Belfast - there's a beautiful scene with a dozen kids who the BBC was trying to track down recently.
And there's William Hartnell - only in two scenes, as Mr Fancy, the barman in charge of the "Four Winds" saloon (clearly based on The Crown, but equally clearly a studio set rather than the real thing), and sixteen years away from becoming Doctor Who: he none the less has a couple of very characteristic moments. His second scene has been Youtubed here and here: look at the way his eyes are moving about 1:25 into the first clip - we've certainly seen that before! - and listen his rant for the first half-minute of the second clip - very Doctor-ish until he uses the unnervingly colloquial word "quid"!
Anyway, a good start to the year's viewing.