I have vague memories of watching an animated film about a young boy (and not much else) who spoke to a voice all through film. I think it ended up he was speaking to himself in the future. Can't remember much else about setting except a black background (as if in space). Think it may have been a Japanese animation. Any ideas?

Sounds like Les Maîtres du temps (http://en.wikipedia.org/wiki/Les_Ma%C3%AEtres_du_temps)

I think that's the very film! It seems to have been dubbed in English by BBC and screened in 1987 and 1991 as The Time Masters. Thanks for your help, I would never have guessed that. Any ideas where I can find a copy of the English dubbed version?