Hi Elspheth
I don't know alot about passports but we have them for all our ponies (not that were going to take them any where just that you now have to have passports for horses) and we got them from the vet I think.
Here's a website that might be useful (don't know if they are).
http://www.defra.gov.uk/animalh/quarantine/pets/index.htm or
http://www.defra.gov.uk/animalh/quarantine/quarantine/regulation/eu_reg.htm
Sophie