May I ask why Virgin operate Voyagers on the Euston to Birmingham to Glasgow route instead of Pendolino's? I know Pendolino's do some of the Class 9 Virgin services but a lot is done with a Voyager depsite the entire route being under wires?
Short answer:
Birmingham - WCML - Glasgow/ Edinburgh used to be through Cross Country services from Devon/ Cornwall etc, back when Voyagers were introduced.
So, Virgin Cross Country ordered enough Voyagers to run services based on the service patterns.
Then, with franchise changes, the route was chopped at New Street - with the WCML section running as part of the Virgin West Coast franchise (who therefore took on a share of the pool of Voyagers - in addition to the London - Holyhead Voyagers that were always required for West Coast services).
All was good for a while (but with diesel Voyagers running entirely under the wires from Birmingham to Glasgow/ Edinburgh).
Then, to squeeze the fleet further, Virgin extended the "EBWs" (Euston - Birmingham - Wolverhampton) onto the Birmingham - Glasgow/ Edinburgh services (saves a unit/ path between New Street and Wolves, so allows a 390 to replace a Voyager which allows a Voyager diagram to be doubled up).
This is all well and good (for some people), but now means that Voyagers are potentially running under the wires all the way from London to Glasgow/ Edinburgh.
It's not easy to get more 125mph tilting stock to replace these Voyagers (e.g. 800s won't tilt)
Even if you ordered more 390s (were that even possible?) then we'll have a surfeit of them once London - Birmingham/ Manchester is run by 400m HS2 services (i.e. not long enough to get your money's worth out of ordering another dozen 390s)
Virgin still need Voyagers to reach the places that wires don't (Chester, Wrexham, Holyhead, Shrewsbury and currently Blackpool), so it may be that they decided it'd be easier to have two fleets (Voyagers and Pendolini) than get in a third fleet to replace the "Voyagers under the wires", since they'll still need Voyagers on services to Chester etc.
Okay, that wasn't a short version... sorry! Maybe the really short version is "there isn't anything more suitable, given that 125mph WCML services need to tilt, and no 390s on the horizon - especially given that the WCML franchise keeps seeing piecemeal extensions that keep deferring the big questions about fleet replacement/ enhancements)
What's worse is that the decision on WCML stock and the electrification of the MML both really need to fall into place before replacement / additional stock for Cross Country can be sorted out, so us passengers on XC are even further away from seeing some decisions made.