Well said davejb, a pressure check must imply that a pressure guage is used, I forget to mention it in my earlier post but I assumed that a guage must be employed. I am very surprised that they aren't on the Nimrod. If they aren't used I am not surprised that the pipe system is checked by listening for whistles which implies that compressed air is merely blown into the piping system which would not apply any pressure to the seals. They should, ideally be pressurised to 150% of the safe working pressure, if the manufacturers do not recommend this test they may well be afraid that the system cannot meet this test.
I well remember RAF posters in my day quoting "Don't assume, check", and I am guilty of that.