The longest Varsity sortie in my log book was 5:20 out of Machrihanish in the summer of '69 (Ex Strong Gale - an ASW ex in which (IIRC) we spent our time patrolling the North Sea and then returned to Mac!). I was on a refresher prior to MOTU so was 'co-opted' to be co for one of the QFI's on 5FTS.
I must admit I thought the barrel roll incident was later 'cos I remember seeing the ac in the hangar in Jun/Jul 68 with the engines drooping and being told:
1. Never Barrel Roll a Varsity.
2. If you do don't chicken out.
3. If you chicken out don't pull too hard.
4. If you pull too hard own up on recovery (if you recover!).