class 156?
150?
It looks to me like the window for the toilet of Sprinter in Serco-Abellio Northern livery.
Class 153?
321/322?
I'm reasonably certain that's a Northern unit, but what Northern stock is newer than a 322 and still has metal window frames?
I guess, just possibly, it could be one of the newer 319s?

ok I'm utterly baffled now
Mark 5 coaching stock?
not a 158, no
No, not a 150150?
Yes, that's the one!319?
No not a Mk3...mark 3 coach?
No, you don't often find fuel tanks on coaching stock...Mk I ?