Now that's the strange point.

I only have one printer, the XP-630 but when I go to ControlPanel/Device&Printers the printer appears twice. Once as "EPSON61E3E9 (XP-630 Series)" and then again as "EPSON XP-630 Series (Network)".

Initially I had the former selected as default and with this setting there was no A5 paper listed in Word.

I then changed the default to the latter and to my surprise the printer works OK (simple test) AND the A5 paper is now included in the lists of paper in Word.

Beats me but I am now happy that I now have my A5 paper.

Once again thanks thanks to both of you.