My approach (and I'm planning on keeping the card so I won't be able to try it out myself) would be to make sure I put no further spending through from one week prior to the anniversary date (in case the transactions take a while to post). In this way you can clearly say you have received no benefit from the card and as such request a full refund of the £99 annual fee if they try to charge it, stating that you have only kept the account open to fulfil the T&Cs of the free night voucher (you could always drop them a secure message in advance to put this in writing). If they then refused to refund the year 2 fee I would advise them to reconsider or you will take the case to the FOS.