Slightly pedantic.....you don't need a JAA class 2 if you're studying for the NPPL and there is no point at which you have to state what you're studying for.
Therefore, you can get your GP to do you an NPPL medical and fly solo on that. It's very similar in standard to the HGV medical so I would have thought you'd be alright.
However, if you do want the JAA PPL then you will need to get the JAA class 2 as stated above.
I'm suprised that you CFI hasn't mentioned this....it's one of the first things I advise a student to get sorted as you could have some medical condition which may mean you cannot hold any form of pilot medical and will have wasted all that money! Unlikely, I know, but possible!
Have you read and signed the school Flying Order Book (local orders) as well. Some schools would require this read and signed before solo as well as the Air Law exam. Medical is the only legal requriement though.
Duchess