Summer Saturdays in Anglia land used to see plenty of pairs of 31s on holiday trains. Usually it was the Birmingham - Yarmouth that would produce as well as trips from Liverpool Lime Street later in the 80s
Yes, happened quite a lot when Type 2s or 3s were rostered for a train which really needed Type 4 level ETS. See also North Wales coast circa 2000 when 2x37 were booked for a Sunday afternoon turn from Holyhead to Birmingham connecting with the ferry. I also remember one snowy winter in the 1990s when pairs of 31s were put on the normal loco hauled turns in case of failure.