A few from the Airedale line in the 90s/early 2000s.
1. WYPTE Class 144s working to Carlisle. Usually these were coupled to a 156 but there was a Saturdays only service in summer that was booked to be one. The best I remember travelling on was a pair of three cars on a service back from Carlisle.
2. Tyne & Wear liveried Class 142 working Leeds - Morecambe. I have a picture of one at Hellifield somewhere.
3. A WYPTE Class 155 working the evening Leeds - Ribblehead. I seem to think it may have terminated at Hellifield due to engineering on the s&c. Crewing must have been a challenge as it was planned for a Skipton crew who didn't sign them, presume a Leeds crew worked it through.
4. One I didn't see but heard about was a Carmine & Cream Scotrail 156 working a Carlisle - Leeds. This was the result of a problem that trapped the Northern unit that worked the morning Dumfries - Carlisle North of the border, and I assume the Scotrail unit off the morning Newcastle - Glasgow was borrowed, since it would be trapped at Carlisle. I think the trapped Northern unit may have made it to Glasgow that day.
Wasn't a Strathclyde 156 involved in the Ais Gill accident in 1995? Either directly involved or used as a "rescue train"? I vaguely recall seeing the orange on photos and news reports at the time.
Or is that another false memory?
I think you are right, one was used as a rescue train. I distinctly remember the reporting on Channel 4 the night after and being surprised at the appearance of a Strathclyde 156 in the background. I wonder if it was used to get media to the site as well.