Vanstmic, the dealer will do a run-out test on the wheels, send the stuff over to BMW UK and then they decide (not the dealer). If your car has been in the BMW network from new you stand a much better chance of getting the wheels replaced free of charge.
There is no official position on this from BMW, it's on a case by case basis. My other half has had hire car from BMW for the last week (paid for by BMW) due to there being non stock of 225M wheels at the moment.
If BMW refuse to pay, then you need to look into trading standards/small calims court etc. Of course, this all depends on your individual car and circumstances.