Chris,
I read the inscription just as you have transcribed it... the year I take to be 1919, of course.
Given that the photographer's studio is shown as being in East Ham (East London) I'd suggest that the strongest contender might be
17th Bn, though not definite.
Thanks for the closer image of the cap badge, but it's still a little vague for me to discern any detail that might reveal one particular regiment or another.
Cheers for now,
JT