I suggest researching the degree if its worth swapping for. You might need an A level in politics but I dont know it's for most courses. For law, you dont need any specific subjects so I suggest applying for clearing or if you want to do law at any of your offers unis, you can contact them to switch your course to law - however, it depends the uni since some wont let you like Bristol due to the LNAT and you might need to do something like a new personal statement for law since you do need proof you want to study law at uni or have some interest in it as academic subject.