I have two daughters with dual Nationality. Three years ago the younger one had her British Passport stolen so we had to send her Emergency UK passport which had been issued to her and photocopies of all the pages from the other passport. I started photocopying the pages of the other passport but soon stopped as it had 50 pages and was taking ages ! I called them and they said I could send the actual passport instead of all those photocopies.
My older daughter is now renewing her passport from Canada so has sent both her UK and Thai passports. I am also renewing mine as it is damaged. I only have British Nationality so have just sent my passport. If they have your passport they wont need photocopies too.
Hope this helps !
