G-MADY
Hopefully the 'twang' didn't interrupt your chat
fmgc
I think you have the most likely answer. An aircraft somewhere over the Ocean relatively close to the European boundary asking for some information on the published interpilot frequency. Ducting also happens relatively commonly at other facilities, for example, hearing traffic calling in a French airfield circuit whilst on a UK Tower frequency. It's just an occasional quirk of physics.
Skidkid
Interestingly the only mandatory part of the CAA 'advice' is that the ICAO Doc states that 123.450MHz
shall be designated as an air-air frequency in specific areas. None of the rest of their spiel gives any instruction, merely inferred guidance by raising the awareness of the problems which may be encountered. I assume their UK 'mandate' as to where it may be used comes from the allocation of the frequency in the AIP, or to individual company Ops facilities. If you are not using it in accordance with either of these, then your use is unauthorised.
The CAA SRG semantics on interpretation given to us in ATC are:
Shall, is to, are to, must: mean that the instruction is mandatory.
will: is only used for information or descriptive writing (usually describing a third parties expected actions) and is not an instruction.
may: means that the instruction is permissive, optional, or alternative.
should: means that it is strongly adviseable that the instruction is carried out; it is recommended or discretionary. It is applied where the more positive 'shall' is unreasonable but a good reason would be required for not following the instruction.
I would like to think these appeared somewhere in pilot documentation as well. Can't find them in the ANO or the AIP, but I can't guarantee they ain't in there somewhere.