Thanks for reply.
I have been told by NATS that as the control tower is airside I will need to get a pass from BAA and they don't seem to be able to get them themselves and they say that they can't get them for under 16 year olds.
I am confused by the security pass system because I am currently 14, 15 when I do my week work experience and as I am under 16 it should be easier for me to get a pass because I have no criminal record etc.