Hi Sweb. I've done a bit of preliminary digging re the Spit 22/24.
As I thought, only Number 80 Squadron, R.A.F. were fully equipped with the Mk24, and, apart from foreign users, the Mk22 equipped only the R.Aux.A.F., with 10 of the 'County' Squadrons using the type. None of these units were based at Henley, being stationed on their local county, or City, RAF airfield, for example, Turnhouse (Edinburgh) for 603 'City of Edinburgh' Sqn.
Incidentally, Henley was a 'Hostilities only' training base, a small grass airfield, and closed in 1945. Is it possible that your friend meant Kenley, the BoB fighter station in Surrey? This was operational at that period.
Although none of the R.Aux.A.F. Squadrons were permanently stationed there, it is very possible that one, or all of them, might have used the station for their 'Annual Camp', or for other training purposes. Of course, this still leaves you guessing as to which Squadron was involved. However, if you can narrow down the search a bit, even if it's finding out where the chap lived at the time, that could give a clue as to which Squadron you need.
As far as I can see, there was a transition period in colours and markings for the Spit 22, towards the end of it's operational life, where, perhaps, half a Squadron's aircraft would be in standard Fighter Command day camouflage, and half painted in 'Aluminium'. I should be able to provide a representative code and serial number for a Spit 22 from all or any of the R.Aux.A.F. Squadrons who used them.
Hope this helpds a bit.
Terry.