Not sure what a 54 plate MINI is as we don't refer to them that way here in the states, but if you've got a CVT you need special CVT fluid. Redline makes the correct product and it's supposedly better than the Esso fluid the car came with. DO NOT use regular old ATF in a CVT.
If you've got something other than a MINI with a CVT I'm not sure what it takes but don't assume that it takes ATF- find out for sure before you refill.
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