A broken down class 91? Surely not! (sarcasm).
I believe they're actually quite reliable now, but in the early days it was a wonder if one would make it from Kings Cross to Alexandra Palace (Bounds Green) without breakding down...
Ahh, how much more reliable the old 89 was. AND would pull a 15 coach rake on a wet, windy, cold day from standing start on an up incline... whereas the 91 needed to slipstream HSTs to get going...
The 89, incidentally, was one of the few locos that when light engine could race a 317 up the lower ECML from a standing start. Only an HST light would match it- and even then only just.