If you phone your dealer they'll tell you the exact brand it sould have in at it's service (think it's castrol) and the type. Think it's 0W 30, something like that, don't quote me on it though!

It's a long life oil as the Mini's are only ment to be serviced every 15k! Far too long, but from what I saw in Halfrauds this is about the only oil of 0W 30. About £14 per litre. I had to but from BMW as Halfrauds had run out and was only £1 more.
Anyway, best bet is to contact your dealer to find out for sure, although I'm sure someone on here will put me right if I'm wrong, hope that helps!
James.