It’s a specialist vehicle, with capabilities / equipment that a normal “civilian” fire truck doesn’t have (e.g. foam capability). Therefore, sourcing one, especially at short notice, probably wan’t going to be viable. The timescale, just to drive one across from whatever RAF unit that had one spare, would probably have eaten away most (if not all) of the flying “window.” Cranditz would probably have been AEF flying = no chance to source one from there. Coningsby - fire crew would have been needed to drive one across - depletion of their staff for normal domestic cover if over a weekend.
There are, of course, different size / type fire trucks; no idea of any “compatibility” for FMT600 requirements.
Whilst I would one of the first to have a legitimate “pop” at anything that placed any unnecessary hurdles in the way of getting cadets flying ( had a whinge about it in Wg HQ yesterday!), for this situation, emergency equipment fail = nothing really that could be done to alleviate it.
Whilst a commercial flight (all the pax had been out of their seats, getting baggage down, prior to the aircraft stopping!), when you need the fire services, you don’t want delays or something that might not work!