Actually, BP, the appearance is that here in the UK they do examine the GAR forms very carefully, but only if it is Special Branch (the police) i.e. you are flying to/from Ireland, Isle of Man, or the Channel Islands. In that case, you must work for the IRA
And if you forget to send one in, you get an "interview" the moment you step out of the plane (as I well know).
GAR forms sent in regarding Customs/Immigration (e.g. from France to the UK, etc) seem to be totally ignored. And I can see why; almost nobody used them until a few years ago when there was a big "marketing drive". Where I am based, all the schools used to do fly-outs to France and GARs were never done.