The use of an HST on the daily Blackpool - Portsmouth train was short-lived, but it DID happen. Once it was replaced by 47s + Mk 2s, the service operated with the 47 permanently coupled at either end, and was diverted to run into the Low Level platforms at Portsmouth & Southsea.
To return to the main thread, the VT 158s were used on direct services from Manchester Airport - Scotland, Liverpool - Scotland and Liverpool / Manchester - Portsmouth. For a couple of timetables, one of the diagrams was Edinburgh - Liverpool - Portsmouth, giving a "direct" service from Edinburgh to Portsmouth, albeit with a 45 minute wait in Liverpool!
The Manchester Airport - Scotland services were frequently coupled to a First North Western service running between Manchester Airport and either Barrow or Windermere. The trains generally used to split and divide at Bolton. Northbound, the FNW "bit" (formed of a 156) was on the front, but then ran via Wigan North Western, which means it then arrived into Preston after the VT 158 "bit", which had departed Bolton after it. A timetabling nightmare really!
Obviously the introduction of the Voyagers put paid to this and the 158 diagrams were the ones that were early replacements once enough Voyagers came along.