I did this some years ago and then went on to do the RoSPA version. The RoSPA version is much harder and has graded passes where as with the IAM it's a straight pass/fail. RoSPA test is longer covers everything from country road, motorways and even busy town centres.
Take a look at both but I would really suggest the RoSPA one.
Cheers, John
PS. Well done for considering taking these important steps to enjoy your driving responsibly - Do it now!