I've witnessed some very impressive flypasts during my time ( including the Cranwell F4s), and probably been involved in quite a few. I would opine that there is usually a 'grey' area between what has been approved/authorised, through what will almost certainly get you in trouble, to something potentially dangerous.
Just saw a video of an E3 doing a flypast of Lincoln a few years ago. Probably 1000ft msd or even more. I accept that it wasn't needed at roof-top height, but it looked almost pointless. I know it's not a display, but 500ft msd was as high as it ever needed to be! Snag is who will authorise it. QBF is a tad more involved, but again it's just too high.
Conversely, I recall being at Woodvale long long ago as very skilful Hawk QFI (CM) flew a display, then went over the top of ATC/MASUAS somewhat below 100ft! Looked great and perfectly safely flown. I remember Harriers out in Belize flying even lower, and occasionally upside down!
As ever it's a balancing act. You know if you 'bend' the authorisation you'll probably get away with it - provided you have the skill to safely complete it. If you completely ignore the auth/approval you're going to be in trouble, but sometimes it's worth it and just has to be done.