I doubt if anybody would be foolhardy enough to bug an aircraft, except mayby on the lines suggested by Clancy in 'sum of all fears'.
Any other method would eventually be found, and the political fallout would be, possably, huge.
Remember a few years ago when a load of sensitive papers were found on one of the Peacocks during a service?
Besides, the Brits can get a lot of info from GCHQ so it is belived.