I was recently browsing through O.S. Nock's book
Electric Euston to Glasgow, written in 1974 & covering the electrification of the northern WCML in the early 1970s.
According to this account, developing a seriously untapped travel market between Liverpool/Manchester and central Scotland was a significant plank supporting BR's business case for Weaver Junction - Glasgow electrification. No doubt this was the reason for provision of the lavish post-electrification services mentioned by
@Sir Felix Pole.
As I recall, after electrification the Preston & Carstairs "portion" trains ran about a two hourly frequency through the day. I think the buffet car on these trains always stayed with the Manchester/Glasgow portion and the mechanics of the splits & combinations could sometimes mean the buffet ended up as either the first or last coach in the train, rather than the centre, which could mean a longish walk to buy your cup of MaxPax tea.
At morning and evening "business peak" times there were still separate full-length Liverpool Lime St/Edinburgh and Manchester Vic/Glasgow
* trains, which did not divide en route but were timed for cross-platform connections on platforms 3 and 4 at Preston. The Manchester - Glasgow train departed from Preston first and had the faster run north, while the Liverpool - Edinburgh took off 5 or so minutes later, with stops at more stations along the way.
Actual patronage of Inter-City's enhanced Liverpool - Glasgow services post-electrification never really matched up to BR's optimistic projections.
This had been foreshadowed in Nock's book. He pointed out that, notwithstanding faster electric trains once on the WCML, many of the "favoured suburbs" in Manchester and Liverpool - the source of the prosperous businessmen expected to travel to meetings in Glasgow or Edinburgh - were on the wrong side of town for these trains. Time-poor executives living in West Kirby or Wilmslow would need to change stations in either Liverpool or Manchester city centre (no Merseyrail link & loop, or Windsor Link in those days), so they would be likely to use their car for the whole trip. Same thing applied to Bert and Ada travelling from Crosby or Sale with a heavy suitcase each.
The silver lining to this cloud was that after a year or two, by the late 1970s, BR started to offer attractively-priced promotional day returns between North-west England and Glasgow/Edinburgh in an attempt to fill some of the empty seats. Cue a couple of grand days out for myself north of the border. Standing in a rammed present-day TPE EMU, I look back fondly at the days when you had no trouble getting a bay of 4 to yourself (complete with coffin-shaped table & winged headrest) in a sparsely-filled Mk.2 speeding past the Lake District on a sunny summer's morning for a cheap day spotting around Glasgow.
* Around 1976 or 1977, soon after introduction of Mk.3 hauled stock on the WCML, a "premium" Euston/Glasgow set was deployed on the morning Manchester - Glasgow train and the last evening Glasgow - Manchester Vic., giving the incongruous sight of a shiny, brand-new train of Mk.3s at the run-down "old" Manchester Victoria.
This stock was a Longsight set, and to get it home for overnight servicing, the Victoria station pilot dragged the ECS back towards the Chat Moss route just past Ordsall Lane Junction, after which the train loco took it in the opposite direction along the South Junction line to Castlefield Jn, Oxford Rd and on to Longsight. [[getting a bit OT for Liverpool trains here - sorry]]
