Well....Your granddad has a Mk2 Sten, and the other chap what looks like a No4 Lee Enfield...But neither of them have any means of carrying ammunition...They have no webbing!
The bike he is holding is an Edwardian one...
Possibly Holland....But as for Regt....

I'm sorry but there are no discernible tribal distinctions on him or his oppo!
The L/Cpl behind him has an Arm of Service Strip above his chevron, but this could be one of several, and the Divisional Sign above that is too indistinct to make out any detail. I cannot see any shoulder titles to confirm anything either I'm afraid.
They have berets on, so apres 1943 at least!
The uniforms are 1937ptn Battledress.
Have you any other pics of him in uniform?