Further update. They are from an IVC VR660 2” helical scan recorder.
https://www.labguysworld.com/VR-660_031.jpg
I recall some time ago you posted that you had a reel of 2” videotape but were unable to replay it to find out what was on it. I recall you tried playing it on Paul Marshall’s quad machine with no luck.
Would it be too much to think your ‘unplayable’ tape is this 2” helical format? Is there a machine in the UK you could try your mystery tape on? Have we further opened a can of interesting worms!!