Hello all!
It is a very interesting topic and I look forward to a solution ,it has really caught my curiosity.
Thank you! yes I'm fascinated too, and very grateful for all the replies so far.

Well with regards to his brothers in WW1 - they were all privates in their various regiments and one was a trooper in the Royal Horse Guards. I don't know if my grt grandfather himself fought as he would have been 34 in 1914 and married to his first wife, and I think married men were exempt initially. - I do have a picture of 2 of his bro's in their army uniform and neither are in this picture here.
If we think that this is sometime during the war period, then it could be in Wales, as my grt grandfather moved to S. Wales between 1908-1918.
I agree that it is definitely very informal, some very formal and some the complete opposite! I think my grt grandad looks like he
may have a tie on under his jacket. Thats why its such a mystery as to what's going on in the picture and why it was taken!
Arranroots - what a fab website! yes I'm sure theres the odd ancestor or two hidden on there somewhere!

Thanks,
acceber