Would it not be a better idea for five 3-car class 175s to be loaned to Northern each day to operate the new service and in return (following electrification and DMU cascading) ten 2-car 158s can go to ATW and run in multiple to replace the five 175/1 diagrams. It would be more capacity for Northern than using 185s and Arriva would also gain in capacity with some Marches services going from 3-car 175 to 4-car 158.
That brings up the interesting question of First Class on Northern services.
The 185s have it, but 158s/175s don't.
So will Northern declassify its 185s or market a First Class service on "Northern Express" services transferred from TPE?
The DfT doesn't normally specify anything about First Class, and the fares are not regulated.
But they have specified that transferred services should not be downgraded in quality.
I don't think the WG will part with 175s, at least until the new W&B franchise in 2018 and a new fleet plan.
ATW needs a consistent 3-car service more than anything else at the moment.
There are too many overcrowded 2-car 175s about.