Try this tread, It's one of many
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(
Boot Release Problem)
Your MINI may or may not have a manual boot release cable (it was an option on earlier MINIs), pull up one corner of the base of the rear seat quite hard to release the seat base, there is a ring that you can pull to open the tailgate (if it's fitted), it's in the middle, in front of the rear seatbelt stalks
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