Thanks for your help. It's getting weirder - after posting my question I found a sort of answer on Google. In the update page I double clicked one of the app icons and another small window opens with the option to update. I clicked it and the update pane at the top of the page lit up with the info briefly and then when blank again. I tried another, same result. At that point the 'Update all' button changed from grey to black. I clicked on that and the update pane at the top then cycled through the apps (about 8 to be updated) and then went blank again.
I left the computer to it and returned later and all the icons had disapeared as they normally would and the message 'all apps are up todate' was showing. Checking the my apps page showed that none needed updating.
So it appears the apps may update but that is not shown in the update pane. I'll see what happens next time.