Not local to you (High Wycombe), but I used these guys a few years ago:
http://royalsteeringwheels.com/I had 2 wheels covered, one alcantara and one leather and I was very impressed with the quality and workmanship. Amusingly, one of his main drivers of business was brand new Audis where a re-cover in alcantara was cheaper than ticking the box on the spec list.