There are echoes of The Truman Show and Pleasantville in this movie, in that co-writers and directors Ricky Gervais and Matthew Robinson have imagined a parallel existence whose peculiarities throw an interesting light on our contemporary situation. In this case, everyone tells the absolute truth. This provides some great moments: people blurt out exactly what they think; advertisements confess the mediocrity of their products; the only movies made are dry, pedantic histories.

Gervais is the put-upon podgy loser: the guy who cannot get the girl and whose job is under threat. Until, in a moment of crisis – well, see the title. So far, so good, the film has the potential to explore big ideas. Does always speaking the truth obviate the need for religion, or deny the possibility of romance? But things slowly lose coherence and momentum, as if the film is struggling with its own logic, and there is the shaky assertion that to lie is to be kind. The conceit which provided such good laughs in the first half hour begins to wear thin, and finally, the film succumbs to an underlying sentimentality in Gervais’ pursuit of Jennifer Garner.

Performances are good, with stand-out turns from Rob Lowe as the office sleaze-ball and Jeffrey Tambor as the boss. Some other Hollywood luminaries contribute very well-observed cameos. Garner is attractive, bright and brittle and Gervais is well within his comfort zone. But surprisingly, at a hundred minutes, it feels too long, and one is left with the impression of an amusing film which did not explore its own ideas with sufficient rigour.