Timetable World includes a full BR timetable for 1982. It also has the ABC Rail Guide for 1981, from which you can figure out the pattern.
I also have some marshalling books downloaded from the BR Coaching Stock group on groups.io, from which you can gain a lot of info - all loco-hauled services are shown and in the 80s obviously everything was loco-hauled.
Key: EBW = Euston/Birmingham/Wolverhampton
In summary:
The 1981 timetable was the simplest, most regular clockface of the 80s timetables with this pattern:
xx45 Glasgow (two-hourly, even hours)
xx50 Liverpool (hourly)
xx55 Manchester (hourly)
xx00 Holyhead, Blackpool or Carlisle (varied). Made more stops.
xx10 Birmingham
xx40 Wolverhampton, occasionally Shrewsbury
In 1982 the Liverpool was reduced to 90-minutely (xx50 or xx20 depending on the hour) and the others stayed more or less the same (the odd gap on the xx00)
In 1983 there were more significant changes. The Manchester became xx50 (not xx55) and the xx40 Wolverhampton extended to either Blackpool or Holyhead every two hours. There were also limited extensions to Shrewsbury still.
Liverpools moved to xx00 or xx30 still on a 90-minute pattern in the middle part of the day, but there was more variation towards the peak (e.g. 1030, 1200 and 1330 and 1500 was then followed by the 1600). The Glasgow xx45s moved from the even hours to the odd hours.
There were still a few direct (Trent Valley) Carlisles, Holyheads and Blackpools but no longer in a regular hourly slot.
1984 was largely unchanged from 1983, despite big changes to XC services on the London Midland region (Birmingham - Manchester/Liverpool) that year.
1985 appeared to show further changes, perhaps driven partly by the Glasgows (still odd-hours xx45) becoming 110mph. However, it wasn't just retimings, it was deregularisation of timings and cuts so I suspect other factors were at play too.
Firstly there was the loss of the hourly Manchester service with it moving to a more irregular and less-consistent pattern.
For example, between 1000 and 1600 there were Manchesters at 1115, 1230, 1355 and 1505. I wonder why Manchester lost its clockface service?
Liverpools were still mostly 90-minutely but the timings changed, e.g. departures at 1020, 1130, 1300, 1430 and 1600.
Even EBWs lost pure clockface timings this year. The Holyhead / Blackpool extensions were withdrawn though Shrewsbury gained a two-hourly service at xx40 odd hours, with xx40s to Wolverhampton in other hours. The Birmingham terminators however varied between xx05 and xx10.
In all, a strange timetable witjh more irregular timings which was also mirrored on HSTs out of Paddington with Bristol losing a consistently-timed service in a similar manner to Manchester.
1987 saw a return of xx10/xx40 clockface to the EBWs, though the Shrewsbury extensions became more irregular again. Liverpools and Manchesters regularised to xx20 or xx50 slots, though neither were hourly.
e.g 1020 Liverpool; 1120 Liverpool; 1150 Manchester; 1220 Liverpool; 1250 Manchester; 1350 Liverpool; 1420 Manchester; 1520 Manchester; 1550 Liverpool (with variations on Fridays and Saturdays).
Glasgows operated in a similar mode to Manchester/Liverpools, using the xx00/xx30 slots but not every hour (e.g. 1030, 1300, 1400, 1530) rather than the former regular two-hourly service. Presumably the aim was to meet demand at busy times of day (hence more afternoon departures but a long late-morning gap).
1987 is the last marshalling book for the 80s. From around 1989 to 1993 I used the WCML from Euston as a passenger more regularly and I do remember towards the end of this period Manchester had reverted to a clockface hourly service, now on the hour. This may have been introduced as early as 1989 but without the timetables I cannot be sure. In March 1989 I travelled from Euston to Piccadilly for the first time and that was an on-the-hour service (0800 or 0900, I think) though not sure if the hourly service kept up throughout the day.
From the 1997 WTTs on Network Rail (CC and CE) the pattern in the early Virgin days was still xx00 on the hour (which is what I seem to remember) and hourly to Manchester. Liverpool was hourly at xx05 whereas EBWs had become xx15 and xx45. Glasgow was xx35 even hours, with odd hours terminating at Preston. So by this time (probably since late 80s/early 90s) much of the full clockface service of the early 80s including hourly services to both Manchester and Liverpool and two-hourly services had been regained, albeit on a different pattern.
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