Thanks for all the replies. Its always interesting to go back to basics and look at how other people do things.
The wider fabric is the best option, of course, but choices are limited, and I'm not aware of many suppliers in the UK. The diagonal method looks interesting, but I doubt my maths is up to it.
Ive just tried my first pieced, as in using contrasting blocks, backing. It's waiting to be quilted at the moment. The one that prompted the question is a baby quilt that's got to be finished quickly and simply because I've run out of time - baby is two weeks old already. The backing fabric has a small, busy design, as someone suggested, so I'm hoping that the joins won't show very much.
Wish me luck!