This really hacks me off, some of us mechanically minded types will check the oil just because we have always done it specially if we have performance cars.
I have a Alfa 2.5V6 which has always used 250ml per 300 miles and just accept it as part of owning an Italian car, but when I bought my wife's
MCC I asked the dealer where the dip stick etc was and he looked at me as if I was mad and said "you won't need to look under there" my point being were you ever told to check it when you bought the car because we wouldn't have been if I hadn't asked.
Now the Alfa owners manual says anything upto 1ltr per 1000km is acceptable so thats OK but as far as I can make out the Mini manual does not actually give to many clues as to whats acceptable.
I would be tempted to seek legal advice sooner rather than later, check your car and home insurance because some policy's include it.
Good luck!