The genuine MINI car cover is available from all dealers for £125 inc VAT. Make sure you specify external cover!. They also do an internal one (with the zip motif) and they are not cheap.
I have been using mine for about a month now and it's very good. Cover is mainly silver but has black roof and mirrors and is elasticated in all the right places.
The only thing to be careful of is exhaust heat. Don't put the cover on straight after running the car as the exhaust pipe will mark (not burn luckily) the cover.
Comes in a lovely little MINI bag and the cover itself says MINI on both sides in case you can;t remember whats underneath.
Hope that COVERS it
nc