Thanks for your reply.
Yes, it did rise okay beforehand. I was wondering about the flour and yeast, actually, as I had bought them about two months ago, and even though they were nowhere near the expiry dates I wondered if it made any difference as to how long they have been stored in the cupboard? I haven't heard of Carrs flour - the one I used was Doves Organic bread flour.
I also thought it might have been that a) I hadn't kneaded it properly b) I only kneaded it once. Should I have knocked it back and then kneaded again before making the shapes? c) I was either too heavy-handed with the kneading (my thumb still goes numb and tingles) d) I wasn't heavy handed enough.
All of this leads me to think that making gorgeous bread is a matter of trial and error?