I don't understand what you mean by "radio bleed" so please provide more information. If you mean that your friend's radio was receiving signals that it should not have it's almost certainly down to the radio. Low cost domestic radio and hi-fi equipment is very susceptible to interference from radio transmissions nearby irrespective of the "atmospheric" conditions prevailing.
Warminster is not near any major airport. Boscombe Down is about 25 miles away and I believe that military helicopters operate around that whole general area. However, these are unlikely to have caused any problems to radio reception - I get them over my house all day and have never experienced any breakthrough on my radios.
VHF broadcast stations are on FM and the airband is on AM and this should reduce any possibility of interference 'twixt the two.