More About Traveling with Pets
In addition to the airlines' websites, below, you may also want to check the Independent Pet and Animal Transportation Association website. This is an international trade association of animal handlers, pet-moving providers, kennel operators and veterinarians who care for pets locally, nationally and worldwide.
They even have a tool that lets you find a pet shipper near you (though the vast majority of shippers are in the U.S.)
We've recently learned of a (very specific) service, AirPets that handles only the shipping of pets into the U.K. that some of you might want to look into.
There will be a lot of players in any international shipping of animals and none of them controls the whole process, so you'll need to check with multiple sources multiple times. You can start with the airline you'll be flying on, because they will have their own requirements for transporting pets. The airline will have its own ideas about cage size and requirements, labeling, instructions for feeding, whether the animal needs to be tranquilized, have a recent veterinarian's certificate of health and the like.
Most airlines, especially in the U.S., implement summertime restrictions on transporting pets as cargo. Because of the increased dangers to pets in the hot weather, most airlines will not take pets as cargo until things cool off in the fall. Be sure to check with your carrier if you are thinking of taking 101 Dalmatians with you to London.