Thank you for the advice - downloaded EverSave. However, the question to Apple must be - why isn't this feature included with iWork or otherwise? I'll send the feedback.
I had used to have MS Office set at 3 min backup, due to constant crashing, but this was my first Pages crash - it was costly as I lost three or four hours work. I just assumed it would be there, somewhere in the background.
EverSave will now be switched on permanently - Apple's reputation now has a little dent in it.