Heard it on the Grapevine that preference is given to Liverpool and Glasgow runs but the fact that F and U are unreserved means there's no obligation for this to happen.
Same way you can get a 158 on 35-minute Northern diagrams but 142s on Newcastle-Glasgow via Carlisle ones.
The 11 car intro diagrams aren't given preference to any particular route, more to journeys with heavy loadings.
Many diagrams consist of journeys to different destinations, not just shuttling between the same places all day hence they can be seen on anything.
Equally, some diagrams do involve stock shuttling between the same places all day so if there is one particularly heavy loaded journey, the same unit will stay on diagram regardless.
Not explained particularly well but you get the idea!
I see what you mean, but a return journey from London to Manchester in the middle of the day is unlikely to be busy at all in either direction, whereas anything going to Glasgow will be comparatively heaving.
That's not a great analogy, as I believe the only G&SW service that North East 142s occasionally found their way onto was an early morning Dumfries - Newcastle (or something similar) working that was generally booked a 156. The Newcastle - Glasgow via Carlisle services use Scotrail (SPT units formerly) 156s with Northern crews as far as Carlisle on all services.Same way you can get a 158 on 35-minute Northern diagrams but 142s on Newcastle-Glasgow via Carlisle ones.
Same way you can get a 158 on 35-minute Northern diagrams but 142s on Newcastle-Glasgow via Carlisle ones.