I've bought quite a few tyres from Inner Ring over the past couple of years. They specialise in Performance and 4x4 tyres, and have a pretty good stock available at all times, and the service is excellent. They also do laser alignment and a more advanced wheel balancing than most places.
They're on the road running parallel to The A61 just before you get to that garage selling strange things with a BMW badge mascarading as cars...
When I had a Discovery, they were the only tyre place in Derby that had 3 tyres available in stock of any type, let alone the brand / size combination I wanted. I've since been back with my Passat, and they've had the brand / size in stock I've wanted each time. They've also been the cheapest in the area each time.
Cheers
Ben