Originally Posted by
Misco60
I recently travelled on an Avanti service on which there was no Standard Premium due to the number of first class passengers, so you need to be prepared for the (slight) possibility that you won't be able to upgrade.
Good point. Historically that has only been a limited number of London-Glasgow trains at very busy times, but the new Class 805/807 trains have a much smaller provision of First class seats so the new Liverpool services they are operating are less likely to offer SP going forward.