Other commuters riding too close I have been commuting to work for a few months now, and generally I enjoy it. Unfortunately I've noticed that on the way back (never seems to happen in the morning - I set off quite early) I will often find someone rides much too close behind me, i.e. within half a bicycle length, trying to draft.

I think it is the same person or a small number of people (I ride the same route at the same time every day.)

This person (these people) will ride this close for a couple of miles - there's a fairly long main road with an on-road cycle path. I think riding this close to my back wheel is rude and dangerous because I could need to stop for any reason (car turns without signalling, small child runs into road, mechanical failure).

I'd much rather he kept back or overtook me, but I feel I would catch up and we'd be in the same situation. I'm not going to slow down because somebody is being rude.

For example, I turn off a main road into my village. In one instance I signalled very clearly, well in advance, and after a pause started braking, only to hear the other rider actually skid behind me. That to me indicates that this person is much too close and isn't paying attention enough to do so safely.

1) Is it reasonable to feel that this person is too close and riding dangerously?

2) I'm going to try to say something next time this happens, but I'd much rather concentrate on the road and not look over my shoulder trying to talk to someone who probably can't hear me over traffic. Is there a clear (polite!) signal I can give that will indicate I'd like more space?

Thanks!
Just wave him past, that's what I do. I don't draft and I'm not interested in someone drafting off me. Nor am I particularly interested in being polite to someone who is interfering with my ride or looking around worrying about them.

Waving someone past is a pretty universal hand signal I would think. I use it with cars, cyclists, and anything else.