Anything which uses RF and is used in an aeroplane must be licensed unless it has a specific exemption for such use.
So doesnt that mean it is illegal to use a portable GPS receiver or does it only become illegal if it is transmitting?
Anyway, I've had enough of this. So tomorrow I will be writing both to Ofcom and the CAA to obtain a clear statement which even the most ridiculous barrack room lawyer will be able to understand.
If you get such a statement you will almost certainly find you cannot disclose their statement because it will be followed by a non disclosure - unless of course you ignore their non disclosure.