Hampstead: Diane Keaton and Brendan Gleeson climb gamely up nothing hill

So how far can you get on good will alone? On this evidence, no further than the pretty pastry shop at the bottom of Richard Curtis Gardens. Nobody with anything other than ice in their soul could fail to be entranced at the notion of a romantic comedy starring Brendan Gleeson and Diane Keaton. Just look at that lovely still of them sitting idyllically on Hampstead Heath. Now wave it in front of your eyes for an hour or two. That experience will be richer than anything in Joel Hopkins’s underpowered screen filler.

The film is based – pretty loosely, I’m betting – on the true story of a squatter, Harry Hallowes, who really did win the rights to his shack on the Heath. The charming, muddled Emily (American for no other reason than she is played by Diane Keaton) finds herself in relative financial straits after the death of her English husband. She is so poor she may be forced to move away from stinking rich neighbours to somewhere inhabited by the merely indecently loaded.

Why this should worry her is not entirely clear. Almost all her friends seem ghastly. Leslie Manville plays a snob whose malignity is no more subtly conveyed than that of the posh people in her old pal Mike Leigh’s films. Jason Watkins smarms around her as an accountant with intentions.

Of course, these awful people want to knock down the smelly old Irishman’s shed and build a plush apartment complex. But Diana has met this Donald (for, bizarrely it is Brendan) and she has begun to warm to his case and to him.

Keaton and Gleeson are grand. The chemistry is not quite explosive, but it sizzles a bit. Most everything surrounding them is a disaster. Shamelessly seeking to ape the urban paradise of Curtis's Notting Hill, the film-makers look to have spent as much effort on background colour as on fine-tuning the script. Young people in nice shirts sell bespoke olives in the background of every second scene. Even Donald's self-constructed cabin looks no less lovely than the average trustafarian's shag pad.

In its later stages, as Donald’s court case begins, the film does make some effort to address social inequality in richer London boroughs, but, coming so soon after the Grenfell Tower fire, that plotline ends up feeling shallow and uncomfortable.

Less serious is the strange issue of the male lead’s forename. This writer can attest that almost nobody from the Republic of Ireland is called Donald. The character seems to have been so named to accommodate one bad joke. See if you can work out what it is. (Remember Donald could be described “a tramp”.)