The normal route to the IAM test is the "Skill For Life" package 
At a cost of about £100. Tthis includes the following:
A copy of the IAM's Advanced Driving/Motorcycling Manual
Associate membership of one of the many local IAM Groups
A place on one of their courses to prepare for the IAM Test
The IAM Advanced Test
Your First Years Membership of the IAM after passing the Advanced Test.

As a Senior IAM Observer I'm prepared to offer to anyone I know a free assessment of their driving.

Most people have bad driving habits; you might be surprised how many ways your driving can be improved, yet how easy it could be to make driving more enjoyable and safer, and how to make better progress legally.

Apply by sending me an e-mail