I took my IAM test at 70 and managed to grt an insurance reduction next time around. Go to the IAM wesite for detailed information about the test.
I would recommend it to anyone. You have to have several observed drives, each of about 45 minutes,where you are assessed and your faults pointed out for correction. When the observer ( and I had a different one each time ) thinks you are ready you then apply and take your test, which is with (usually) a retired police Class 1 driver. The test, like the observed drives, takes in town, country and motorway driving, manoevering, parking etc. Then several questions on the highway code.
Oh, and while you are taking the test you will be asked to give a running commentary of what you see etc. You may, as I was, be asked what the last two roadside signs were !
So the course and test teaches you long and short range and all-round observation, so you are never taken by surprise, and anticipate PRACTICALLY everything and anything. In fact, a small deer sprang in front of me onto the inside lane of the M25 ! I was doing 70 and fortunately it darted back up the bank pretty sharply ! Go for it, and good luck - it will only make you a better driver.