Last day at work tomorrow and need away early Help?

It is my last day at work tomorrow and I have received my mortgage offer today and need to make an appointment with my solicitor. I called today and he can only fit me in tomorrow during my afternoon at work. I have asked my boss for a half day (using my holiday entitlement that I am not being paid for) and she has said no. I have asked to change days with my solicitor but he is very busy and the next available day I can see him he said it too far away. Can I leave work early without my boss's say so? Not sure what to do!

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