BPI - if you have some experience, bashing the banks for a conversion would work - we know one or two CFIIs (one of which was a heart surgeon) who tried it with knowledge alone but got average marks of about 67% without using the banks.
If you qualify, you can indeed enrol with the Campaign Against Aviation and book your own tests (at £69 each).
"don't focus too much on whatever books/CBTs are offered by your school"
That depends on the school!
