From February 28, 2000 dogs and cats travelling into the UK from certain European Countries will not need to be quarantined for 6 months provided they satisfy the requirements outlined in the Pet Travel Scheme.

Animals now resident in the UK wishing to travel to Europe (visit the DEFRA website, address below, for the list of qualifying countries) can return to the UK provided they have before departure been:

1. Microchipped. To be done before being vaccinated against rabies.
2. Vaccinated against Rabies. A blood test must then be taken no sooner than 30 days after the vaccination to measure antibodies to Rabies. As some animals do not respond sufficiently after one vaccination it is more cost effective in the long run to give two rabies vaccinations, a fortnight (2-3 weeks) apart. The blood test is then taken at least one month after the last vaccination. There is no requirement to re-test antibody levels provided that a booster injection is given within two years. If the booster is given even 1 day late the blood test will have to be re-done before a travel certificate can be issued.

After the animal has passed the blood test for the first time, a pet passport will be issued. The first date the pet can return to the UK  is 6 months after the date of the last blood test.  Animals can leave the UK before the first possible re-entry date provided a pet passport has been issued. 

Animals returning to the UK will require a pet passport, as well as signed documentation from a vet in Europe that the animal has been treated for ticks and tapeworms within the 24-48 hour period before travel. If the animal is going on a day trip this can be done by an UK vet.

The pet passport is usually all that is required for animals travelling from the UK to Europe. If the animal is not returning to the UK, the rabies blood test does not need to be completed before travel.

Animals in EU countries can apply for a pet passport in their own country, but to enter the UK they not only have to be microchipped and vaccinated against rabies, they must have passed the rabies antibody blood test so that all the necessary parts of the passport can be completed. 

UK animals that move to a EU country do not have to have the rabies blood test performed. These animals can have a blood test in any EU country if they later want to return to the UK. They still would have to wait 6 months after a successful blood test to return to the UK. 

http://www.defra.gov.uk/animalh/quarantine/index.htm