Wirraway;
You would not entirely be incorrect using a Jeep. You could pose it as an American group visitor. There are photos of the RCAF using Jeeps with the Roundel painted on the hood. There is a support vehicle kit for RAF with a starter/battery unit and a couple of other support pieces. It is packaged with Luftwaffe items, I just can not remember the manufacturer right now. I believe it is ESCI but I could be wrong.
As far as truck types. Bedford was another manufacturer that was heavily used. I am not sure of anyone manufacturing currently any British trucks in 1/48.
I know it is not a lot of assistance but I hope it assists somewhat.
Cheers;
Gregory