Thanks for the advice. I found a local place that is just a big room with rolls of carpets to buy as seen. I saw one that's £9/ m2 so a lot cheaper that the bigger shops. They are coming tomorrow to measure up Hooray!
I priced a carpet in Carpetrite and John Lewis an was surprised to find after all the extras were taken into account that John Lewis was much cheaper for a better quality carpet. Ask for the pile density figure (can't remember the technical term) - a more dense pile is obviously more expensive but is less likely to flatten and will wear better.