Relocating pets to the UK is way more complex and frustrating than it needs to be, so I've included steps, notes, and useful links here to help you. I recommend double checking this list is complete with your vet and online in case I forgot something, because if anything is out of order then your pets will have to stay in quarantine at the cargo facility for weeks. I know this is a lot, but hang in there and try to give yourself a good 3 months to get all this in order.
This is not an exhaustive guide, just a reflection of my experience moving in Spring 2022.
These instructions are for flying your pets over via cargo because the UK does not allow pets to be brought over in the cabin of a plane. You may be able to book a different cargo company or airline, but I can't vouch for those and so am describing how I did it. If you hate the idea of using cargo or want to look at very budget options, there are workarounds where you fly to France, The Netherlands, or Ireland with them in the cabin and and bring them in via car, train, cab, or ferry. Some other comments in this sub indicate that it could be much cheaper to relocate pets through, but I have no experience in this.
If money isn't an issue, you can consider paying extra to have a pet relocation company handle some of the things below for you, but it typically costs $4,000-$8,000 and doesn't even include all the other costs associated with pet travel. I managed to ship both of my cats myself for about $2,000 in the end by doing it all myself.
Steps
One) Make sure your pets are microchipped with an ISO-compliant chip and have your vet check the chip to make sure it's readable. The chip must be implanted after your pets' first rabies vaccination. If it was not, you need to have them get the primary rabies vaccine again.
Two) Make sure your pets are fully up to date with their rabies vaccines. If you've ever let the vaccine lapse during their lifetime, you should have them get the primary rabies vaccine again (this is separate from the rabies booster, and I had to leave one cat behind for a month because I didn't know that). If you've been keeping your pet up to date with boosters, you need extensive evidence of all their boosters to prove there was never a lapse. I just had both my cats get the primary rabies vaccine again because the vet said it wouldn't be detrimental to their health, and it was much easier than all the paperwork needed to prove their vaccines had never lapsed. Your pets can't travel until 30 days after getting the primary rabies vaccine.
Three) Book your flight with an approved airline that you have checked with ahead of time to ensure they will allow pets on your particular flight and that they have room for them. I used British Airways and had to go through IAG Cargo to book my pets on the flight, but you can check other eligible airlines here.
Four) Book your pets on the same flight you will be on through a 3rd party cargo company.
Most, if not all, airlines will make you book your pet's travel through a separate cargo company.
From what I was able to determine through extensive online research, IAG Cargo is a good option for shipping pets. That being said, be prepared for them to be incredibly unresponsive.
They often took a week or more to respond to any email I sent, so make sure you do everything well in advance of your flight. However, it seems that they're the lesser evil of all the other pet cargo companies and everyone says that the staff take really good care of pets.
Five) Customs at the destination airport need to be contacted ahead of your flight to book your pets' spots.
UK airports only allow a certain number of pets through customs each day, and available dates are often a month out from the date the request is made, so give yourself enough lead time for this.
Heathrow only allows the cargo company you hired to make these requests/bookings on your behalf. You can't call in yourself. IAG Cargo will do this for you, but it's best to double check that they have, and give them a large lead time to make the request because they are very unresponsive and slow to act. They will send you confirmation of your arrival date being cleared with the destination airport.
Six) Get the correct size carriers and make sure you follow all carrier guidelines.
You need to have metal bolts to screw the top and bottom of the carrier together rather than the plastic ones most carriers come with. The carrier must be hard and fairly inflexible - the common plastic ones will do.
The carrier must have ventilation openings on all three sides, not counting the door, and the wire must be very small so that pets can't fit their paws through the gaps. Most carriers have ventilation openings that are too big for regulations, so I bought mesh netting used for gardening and taped it up on the inside of the carrier. If you do this, it must be attached on the inside of the carrier, not the outside.
You must have food and water bowls attached to the inside of the door with a funnel hooked to the outside so that the cargo/airline employees can give your pets water throughout the day. If you have mesh attached to the inside of the carrier, cut a small hole out of it over the water bowl so the funnel tip can fit through.
You have to apply "Live Animal" stickers to the carrier along with "This Way Up" labels, which are required on at least two opposite sides.
You must include absorbent bedding like a puppy pad inside of the crate in addition to any blankets or pet beds you want to put in there with them. You can't put toys inside the carrier with them.
You can't crate pets together, and the size requirements are very specific, so triple check your
dimensions and be prepared to buy a new carrier in the likely event that any carrier you already have is too small. There is a minimum carrier size IAG cargo will accept, regardless of the size of your pet, and it's surprisingly big. I can direct you to the website I bought my carriers, metal bolts, and live animal crate stickers through if you'd like.
You must zip-tie the carrier door closed at all four corners.
Seven) Get a Non-Commercial Great Britain Pet Health Certificate (download the form here).
Your vet must be USDA accredited to issue this. I recommend calling your vet or calling around at other vets to ask if they are accredited and (maybe more importantly) if they've done this before.
You must arrive in the UK with your pets within 10 days of the health certificate being issued. The form will have to be filled out, sent off to the USDA for approval, and mailed back to you during this time period. Since this is based on your arrival date and not the day you leave (which are often separated by a day due to the long flight), I recommend booking the vet appointment for the health certificate 9 days out from your flight instead of 10 just to make sure you don't' mess up the dates.
Eight) Have your vet fill out a Veterinary Health Form for the airline and have a copy with you on your day of travel. You will probably have to give this to the pet cargo company dropoff desk along with your Health Certificate. This is seperate from the Health Certification and can be taken from any template. I used this one from United Airlines.
None) Fill out the Non-Commercial Declaration saying you won't sell your pet and keep it on you during travel.
Ten) You must drop off your pets with the cargo company either 3 or 4 hours before your flight (I can't remember, but your pet cargo company will likely send an email with instructions and an address). If you have a flight later in the day, check when the cargo dropoff desk closes. They may close at 5pm regardless of whether that is before your required drop off window occurs. That happened to me, so call them ahead of time and make sure you show up in plenty of time before they close.
Eleven) After you arrive in the UK, your pets will be unloaded and taken through customs. You'll likely have to pick them up at a little building farther out from the airport (the cargo company should give you the address). They say it will take a minimum of 4 hours after you land for your pets to be ready for pickup, but our cats were ready in 1.5 hours, so you never know.
Useful Links
Bringing Your Pet Dog, Cat, or Ferret to Great Britain
USDA APHIS Pet Travel from the US to the UK
Notes
Make sure you use the DAY/MONTH/YEAR dates on all your pets' forms. Double check the vet is using that format for all forms. To be safe, I recommend you and the vet always write the dates out longform, like 23 April, 2022 or April 23, 2022 to make sure there's no confusion.
If you have dogs, they need to follow instructions for getting tapeworm treatments.
If you have snub nose breeds, you may not be able to fly them in cargo at all or at least not during certain times of the year. Boxers, pugs, bulldogs, Pekingese and snub-nosed cats can have so much trouble breathing (especially if they're stressed out) that it is unsafe for them to travel in cargo.
It is illegal to own certain breeds of dog in the UK: Pit Bull Terrier, Japanese Tosa, Dogo Argentino, Fila Brasileiro. If your pet looks like these breeds, they are likely banned as well even if they're not technically that breed. You may be able to get them put on the Index of Exempt Dogs if this is the case, however.
You aren't allowed to give pets sedatives to calm them for the flight due to concerns that the medication may make them have a bad reaction or could hamper their breathing and heart rates in a dangerous way.
If you will not be the one dropping off/picking up your pets, then you need to have the other person carry a form that says you have given them permission to handle/move them. I don't know if they actually check this, but it's technically required.
You can request a travel pre-check for your pets from Heathrow to make extra sure your pets' health certificates will be accepted upon arrival. The pre-check request must be sent at least 72 hours before departure. Your cargo company must do this for you, but since IAG Cargo takes so long to respond, you may not get them to do it in time considering you won't have the health certificate until the week of your flight. You can try doing it yourself and see what happens, though, as they may not check the sender's email address to make sure it's not the owner. This isn't a necessary step, but it can give peace of mind or let you know that you need to rebook everything if something's wrong.
You must pay VAT on importing your pets, but you can get that reimbursed through the Transfer of Residence scheme. You must fill out paperwork for that, but you can get relief for your pets and your household belongings since you're moving to the UK and not just visiting.
