Please Help Self Study

Does anyone know if there is any way in which I would be able to self-study some GCSE's and A-Levels simply through use of textbooks purchased on Amazon and then eventually be able to sit the exams at a centre at which I do not normally attend? I am currently studying Scottish qualifications too but remain keen to supplement poor scores in National 5 exams with better results in English qualifications... Any help would me greatly appreciated, Thanks