Got an email from Humax today. Not a bad turnaround as I sent the query on Friday.
As I expected I need to reformat.
"The issue is typically caused by a corrupt index on the hard drive and was not a result of the update.. Unfortunately you will need to format the hard drive on the unit and this will unfortunately remove your recordings. Formatting the Hard Drive does help with any issues with recordings or playback issues
Press Settings on the remote.
Scroll to System Settings and press OK
Scroll to Storage and press OK
Press OK on HDD
Scroll to Format Hard Drive and press OK"
I have informed the boss and she is OK with that but needs a few weeks to watch anything important. I will have a last look at BBC Dinosaurs in 3D with my daughter too!