If the AFS goes on strike at any Airport, public transport flights have to be suspended - Manchester was one example - back in the 80s. Some cargo and private flights might be able to continue to operate from such affected Airports. As has been mentioned before, the Airport Fire category is not dependant on the outside fire service. In this (legal) respect, the coinciding of both Airport and FBU strikes is academic - but permitted operators would obviously be wise to consider the additional potential risk of flying to/from an Airport where the only available fire cover was provided by the thinly spread military. My guess is that Airport Authorities (The BAA on this occasion) may also consider closing their Airports to all flights, due to the prevailing circumstances.