When I applied I only had the one medical so I am not too sure about the CAA medical @ Gatwick.
The NATS medical is apparently more stringent than the CAA one.
What it involved:
A hearing test
A Cardiogram
A Urine (drug and alcohol) test
A vision test
A general look over for good health
NO NEEDLES!!
If the time is there before you start at the college then a medical should be carried out, if it is not then it can be arranged in your first lot of hols after the basic course.
Hope this helps