rorya:
safe mode made no difference.
I discovered that the problem was only with some spreadsheets.
nappy_d:
some were on a network share, some local.
I have actually solved (well a user from another forum did) the issue:
It depends on which printer you have set as default.
In this case a network printer (that, thinking back is notoriously slow at bringing up it's properties).
When the default was set to another printer (in this case a small PDF creator) the sheets opened up at lightning speed, as the other programmes did.
A strange solution, but one that is now stored in my library!
Thanks for your time and efforts