I also live in Cumbria and have an sd SE, got an SE because Cumbria CC like their chippings on the road. Tracking, mine wore the inside edges off the rear tyres (20" 214's with Bridgestones) had the same problem with my previous 535d, Batemand got BMW UK to pay for a full lazer alignment. Nothing was out of BMW talerance but they adjusted it to be right in the middle of tolerence. Swaped to exactly the same NONE runeflat bridgestone tyre (Gates Carlisle) and have done 14k on them and when i was under it at an oil change earlier this month they were wearing perfectly square.
Runflats are crap for Cumbrian roads, loads of problems, its to do with teh camber on them for drainage.
Price wise, its 2/3 hours then the charge for the machine, but they are none too busy so do some horse trading!!