We have had no trouble taking our dogs back and forward between Spain and England. It used to be a bit tricky with only a 48 hour window to get the vet to sign the passport saying the worming/tick treatment had been completed but that window has now been extended to 100 hours (I think) and only worming is now needed, not tick treatment to enter England. Also make sure your dog's rabies vacc. is up to date. We recently took four three month old puppies back to England with no problems. Only trouble was in England where one of the female puppies (and it said female on her passport) turned out to be a boy. Thankfully the new owner saw the funny side.