I thought I read on pprune a few months ago that, now that the Green Goddesses have all been sold to third world nations, the military will not be used to provide cover if the fireman go on strike.
Instead apparently civil companies, such as Serco, are on a retainer to provide such cover. Indeed I believe someone said some oldish (but much newer than GGs) fire tenders were parked at Waddington for use by the civil company if so required.