Despite the average score this is an easy film to watch and one that I very definitely enjoyed.
The plot is simple but even the elements that are predictable have a unique feel. Most interesting is that the viewer is allowed far more information than the people in the film can know yet never given enough to predict more than broad plot movements.
More relevantly, and one of the film's two strongest elements, is that the characters in the film feel very true to themselves. They react as you'd expect them to react, and even when revealing a new element to their character it aligns to what we know already rather than conflicting or feeling contrived.
Sadly the characters to whom that doesn't apply are two key elements of the latter half of the film, which did detract from it.
The writers do however redeem themselves with a succession of one-liners, often dry observations delivered deadpan that made me laugh because of their context or their wit. This is very British humour and made the whole film worthwhile.
The film felt exceedingly low budget, with the lighting, coverage and sets all bare bones - but also all entirely adequate, serviceable and authentic (within context). The lack of budget did however come across in the preparation and filming of the few action scenes, all of which were poor. Rather than choreography and acting that matched the sardonic realism of the rest of the film they fell into a weak pastiche of slapstick, both failing at that but also entirely out of kilter with the rest of the film.
It's a shame, as it let down what could otherwise have been a good film. Watch it anyway, the writing deserves that and there is much to enjoy.