Well, what's wrong with the title "Separate Lies" (accused elsewhere of not being "exciting"). It's cunning, subtle and a bit poetic. (Of course there's a Phil Collins song and a James Belushi film called "Separate Lives", which are alluded to here.)
But the real point is the ethical dilemmas of telling lies at different levels that the film probes. OK, it's not an "in-your-face" hilarious title, but then it's not an in-your-face hilarious film. Please give British films like this a chance. They do try to make people think about important things, as here: how far do you go to protect your life (even if it is a bit rotten) against unexpected disaster. Maybe you tell lies. Maybe you ignore your loved ones' lies. That can wear a lot of people out.
American movies on this theme are abundant, but they usually go much further by involving the use of firearms, which are not a part of everyday life here in Europe.
Maybe we're not so "exciting" over here, but we don't expect slogan-like film titles for films that are not aimed at a massive public.