Here is what I believe to be the first photograph of my Grandfather in uniform (other than perhaps that which appeared in his army paybook) . He is the first seated soldier on the right in the second row.
A bit of digging and thanks to the thoughts shared by members of the British & Commonwealth Military Badge Forum, it would appear that this photograph was indeed taken early in the war, indicators of which include the absence of webbing and the nature of the service uniform worn by the corporal in the centre of the shot. The cap badge is rather obscure, but from its outline, it can be determined that these men are of the North Staffordshire Regiment, as I would expect.
It could be that this photograph was taken at the Lichfield Infantry Training Centre (I.T.C.) in early 1940. He was transferred to the South Staffordshire Regiment in June of 1940.