Just got from a reliable source of mine that retained firefighters are also on strike, apart from the 10% that are in a different union.
Not correct. All retained firefighters have their own union which has a no strike policy and they are therefore working normally.
While licensed civil aerodromes are required to have Emergency Orders that include plans for calling out the local authority emergency services, the Aerodrome Category (CAP 168) depends only on the AFS capability. Local authority capability is not considered for the Aerodrome Category.