The Glasgow-Euston numbers are encouraging, but the real issue with that 50m target for 2026 has to be capacity across the wider WCML. New stock seems unlikely, so the core network is going to come under a lot of pressure – is another 10m on the existing services/stock feasible? As others have said, the pressing need has to be for more services between Euston and Preston/Lancaster – ideally offering as close to a 30 min frequency as can be managed with limited paths. Glasgow services are fine as they are – the 4 and a half journey is competitive for many (like me) who can’t be faffed with heading to Glasgow Airport then trekking into London from Luton or Heathrow. But I’ve been on too may southbound trains that have left Warrington with folk standing – Preston, Wigan and Warrington deserve better.
Blackpool/Preston extras tend to have lower passenger numbers than Glasgow services but unless you are a regular user you could easily board a busier train. The easiest way to avoid what you have described would be to remove Warrington and Wigan calls from Glasgow services when there is an extra service running during the hour. That way Warrington and Wigan continue to be linked twice an hour with each other and Preston but passengers are transferred away from Glasgow services. Two stops add the best part of 10 minutes to journey times, it's not a huge difference but it would be a step forward. 2/3rds of people fly from Glasgow and Edinburgh to London, even excluding people transiting onto other flights the WCML and ECML journey times are not competative. The VHF timetable was designed to decrease journey times and balance passenger numbers. Removing some calls from busy services when alternatives are available is a continuation of that. It's not unreasonable for Wigan and Warrington to only have one fast service per hour to London with irregular timings + the London-Birmingham-Scotland service. That would still be a good service. If it is insufficient then Northern should run a service WCML only service where and when paths are available.
Regarding dropping the calls at Warrington Bank Quay and Wigan NW from the present London - Glasgow via Nuneaton (ex Trent Valley Railway), these trains at this moment in time provide reasonable connections at Warrington BQ from points north of Preston into the present day Manchester - Llandudno Junction/Llandudno/Holyhead via Frodsham and Chester.
Has any thought been given as to how to maintain those connections from Preston and points north?
The journeys you describe are not major passenger flows and Manchester-Chester frequency doubles in May. It's reasonable for Wigan and Warrington to be linked with Preston on a half hourly basis i.e. the via Birmingham service + Preston/Blackpool extras, with London-Glasgow via Trent Valley services only stopping to fill in the gaps left.