Thanks for the reply. I think thta's got me on the right track but not quite sorted yet.
I went where you said but then Customize View - Reset Current View. This has restored the Default view ie: Today, Yesterday, Last Week.
However, I use Follow Up Reminders and when I now try to reset the view to put my Reminder Flags at the top of the page, it goeas back to the 3 Groups again:- Reminders at the top (correct) then 2 Follow Up Flag groups with today's emails at the bottom again!