The Manchester Regiment were a Machine Gun Regiment some times other soldier would call them Gunner as in machine gunners.
There are 3 cap badges in the pic two to the Manchester Regt one looks like the pre 1922 Manchester Regt cap badge and the other is the post 1923 badge, the other one is Royal Pioneer Corps but it could be to the Labour Corps 1917-1922.
The "pre-1923" badge is in fact the Manchester Corporation Transport badge, possibly his pre war employment?
regards