FJJP
The allocation of the assets is done at MOD level within a joint manned office (and some ROs). The detailed planning is done at Andoversford, again joint office but a fair representation of light blue) and the Transops are issued by a small office at a secret airbase not far from Carterton. The final office is entirely light blue current/RO. The problem you seemed to have had at IOT is getting the asset at all. The problems that other readers have had is that of where the assets go to. Your issue was definitely at MOD level. The others at Andoversford level. It is also true that the potential airfields that we might use are their own worst enemies. Without wishing to bore everyone here are a couple of issues.
VC10s carrying pax need Crash Cat 5A-only BZN( AND FFD AT THE MOMENT) have such cover-enhancement costs so who pays?
Leuchars for example will open outside normal ops ( and up Crash Cat) for their own people but not Army moves so we use Edinburgh-a lot more cost but not Leuchars' !
On a recent recovery from the States we were happy to drop our pax at Waddington but one of the problems was that it would not open.
Where possible the system does try to deliver formed units to their nearest airfield but this is on special routes not regular runs.