Just a quick feedback. Before changing registry entries with Brink's suggestion, I thought I'd try the option that Flatiron has his set to. This did what I wanted. I was notifed of updates and the exclamation mark icon wasn't present next to the "Shut down" button. This meant (I assume) that I could shut down without installing any updates.
I had to wait a few days to get notified of updates before I could tell if this did what I wanted. I installed all the updates that I was notfied of but with hindsight, I should have left one off just to see if it was still reported on re-boot. I'll have to wait for the next lot of updates but it seems that this option does what I want
I misunderstood the option I originally had mine set to and should have chosen the one that Flatiron suggested instead