Paul this will not be possible to implement across Airnav. The 7000 series are internationally agreed ICAO codes used throughout the world for specific discrete functions like emergency. Civil and Mil aircraft just flying around use codes allocated by air traffic national authorities. There are multiple codes (hundreds) and they are specific to individual countries. Hence they could not form an worldwide Airnav based alert system.
Your best bet is to find websites that give UK squwak allocations and to identify any batches that are pertaining to your area and are predominently military (for example batches allocated to RAF Coningsby or London(Mil)) and . You can then add these to your own alerts list under the squwaks heading of alerts.
