It is an appallingly scary book: it gave me horrendous sleepless nights for weeks. I agree with eldritch that the 'Ours is not to reason why' reference is unsettling. His constant assertion that 'the powers that be will get through', though, is much more upsetting. Jim's faith in the idea that society, politics and democracy will always make sure that everyone's okay is made to seem so naive in the face of what is so obviously the contrary. Gentleman Jim, though, is far from being a comfortable read either. Jim, a lavatory attendent, doesn't understand why he can't get a glamorous or well paid job like the ones he reads about in books from the library. Every job he sees in the paper needs 'the levels'. He finally decides to be a highwayman, acquires a donkey, and positions himself on a motorway to hold up the cars.
His desperation for glamour and excitement - and his inability to understand why the world isn't like it is in books is touching and pathetic. The faces of authority, though, are petrifying: the traffic warden who has a blank face except for a small, Hitler-like moustache is particularly scary. The judge at the end - who snaps and sentences Jim to be 'hung from the neck until he be dead' is as powerful a depiction of the brutality of society to the common man as any I have seen. Raymond Briggs has not, I don't think, written anything exactly 'nice'. Even Father Christmas is fairly unstereotypical in his general churlishness.
Briggs certainly seems to have some unsettling things to say about the world, but all of it is pretty firmly backed up by a belief that the people are more important than institutions. I bet he's a great guy.