Gordon Bennet
The book by Croucher that you speak of is great as a supplemental, however, only that. A full course of notes is important as well as the very important feedback questions which show all the tricks in the exam questions!
Raven 14
It all comes down to whether you have accrued Multi Crew time, 500 hours being the magic number. If you have this then you can complete the JAA ATPL exams without attending a course, however, most need the course to get through the incredible amount of knowlegde. This knowledge is not about everyday flying either.
Good luck