There has been alot of confusion lately about how early you can do the PETS process before the move. Many people think that you have to do it just 6 months in advance and can't do it earlier. This is not true:
http://www.defra.gov.uk/animalh/quarantine/pets/procedures/support-info/blood.htm"Further blood tests
No further tests are required after the first test which gives a satisfactory result, provided the pet is subsequently revaccinated against rabies by the “Valid until” date on the PETS certificate, EU pet passport or third country official veterinary certificate. If there is a break in the specified vaccination programme, a further blood test will be required after re-vaccination and the six month wait (see below) will apply."Its just that most people don't do this too much ahead of time because they don't have plans that far ahead of time I'm guessing. I did the process in 2003. I just have to show all the records since then stating they've had their rabies vaccination before the previous one expired. The valid until date they're talking about is section IV (Vaccination against rabies), "Valid until" and its the date the rabies vaccination expires.
The thing you will have to do more than once is get a certificate filled out if you do it more than 4 months ahead of when you move. They are only valid for 4 months.
Just check DEFRA's website. They have all this information, you just have to read it clearly and carefully so you don't gloss over any important facts. Also, you can call DEFRA directly with questions.
PETS helpline
Telephone: +44 (0)870 241 1710
I will give them a call on Monday to verify this info.