[humph]

If this isn't the case it may be that you have a none return valve in the pipe that has stuck closed. These have failed on other cars I have owned and I guessing the MINI has one. It's a small inline 'valve' that is usually found in the area where the single pipe from the reservoir splits into two to go to the jets. They are usually only a few pence, just pull the pipe off either side and replace.