There is another way.....
Many airlines will let you travel around Europe particularly, with your "small" pet in the cabin but not into the UK. So...you can fly to say Paris, and then get someone to meet you there with a car (you cannot travel with animals through the chunnel unless they are in a car), and drive to Calais to hop on the Eurotunnel. In fact there is a company that will meet you in Paris but I enquired some time ago and it was £1000! So, get a mate to drive down? You can also do this from other ports, Amsterdam/Rotterdam-Harwich ferry but it takes 6 hours with the animal locked in the car. Calais is the way if you can chance running the gauntlett past illegal violent criminal immigrants. But it is all in all another fine example of how the UK make something so simple so complicated?