You do make a valid point. As far as I am aware there are no compulsory subjects in AS/A levels. You should be able to not take GP. Try to reason with your teachers. However, I will recommend you to take subject like English language, English literature or GP because they help you improve your writings.
But how does it make difference when someone takes GP or not? Either way, we will have to take English language test and it is going to be the determining factor, isn’t it?
There are no compulsory subjects in AS/A Levels. However, its recommended to take one subject in writing. Also, you are not bound to 4 subjects. You can take as many as you can.