Hi Alex.
I found this site that says their was one Gladiator N5820, ex 237 RAF sqdn.
http://surfcity.kund.dalnet.se/gladiator_raf.htm
Look under SAAF Gladiators
I think it is a typo, and may be 1 SAAF as it is found there.
Unless it was a sqdn hack it would be unlikely to have only 1 Gladiator
used operationally.
I have only one shot with coloured Hubs and that photo is same source as 3 sqdn ie Whelan.
Makes it more likely that it was taken with him in 3 sqdn.
It does not show the serial.
If you have photo's of Gladiators in the UK it may show the coloured hubs.
Stefaan