[nuyt]

Stellan, I guess it's a factory picture showing a prototype. The "crew" all seem to be wearing overalls, and yes they are wearing British tin helmets.
The gun? Looks like a French 75, but if this is the Vickers factory, well, they had a lot of types there to work on...
If this was a commercial design meant for export, they would do a lot to make the picture as international as possible.
This tractor (note different running gear as opposed to the other pcitures) was used by Belgium as the T13 type 1 tractor and produced in Belgium under licence.
Portugal seems to have ordered Vickers tractors. Have you come across a picture yet?
Greetings
Nuyt