IKEA
It is NOT allowed just to buy the books and sit the exams, you must enroll with an approved school and do the course work with them before you are signed off, then you apply to the CAA (through your school) to sit the exams.
The exam centres are in Glasgow, Oxford, Gatwick, Silsoe and Orlando. So my friend you will now see that it is not possible to do it the way you suggested, you WILL need to enroll with an approved school.