Asking the boss...
I've just been offered a place as a SATCO, and have been told by NATS that my current employer will not be contacted prior to me giving the OK. Seeing as I have been offered a Jan 2004 start date, this could be sometime away, so I assume they'll contact my other referee sooner, then get the employer reference closer to the time. If you're really concerned, phone NATS HR department, I found them really helpful. Oh, BTW, I am outside the age limit, but have a pilot's licence and an aircraft engineers licence, which was acceptable as a solid background in aviation.
Good luck,
Steve.