Just a quick note on costs, in case anyone's interested. I'm trying to budget moving costs, so it helps me to know what to expect. We're travelling from Seattle, which makes it a bit more difficult.
BA do not at this time have approved PETS routes from the West Coast of the US, except for LA. They quoted me a price of US$20.88/kg, plus about $200 in extra fees, for sending my two labs over via cargo from Seattle and licensing them into quarantine with a view towards early release (
http://www.defra.gov.uk/animalh/quarantine/pets/procedures/support-info/earlyrelease.htm). That makes for a total of about $3200, plus quarantine fees and the emotional distress of quarantine.
The other thing that all airlines do is that they'll charge you based on the volume rather than the weight alone. For instance, though my dogs weigh 90 and 75 lbs, for a total of about 75 kg between them, the crates that they'll be using are so large that they'll actually take up more valuable cargo space than is represented by their weight. So, the airlines use a nifty formula ((height in inches*length*width)/366) to come up with a "volumetric weight" in kg. In our case, that's about 150kg for the two dogs (or twice their actual weight).
However, I called Virgin and got a much better rate travelling from San Francisco under the PETS scheme. They give a discount for shipments above 100kg, so the total is much less. For two dogs, it'll be about $1500 plus GBP210 in PETS scheme fees when we arrive in the UK. Alaska Air will fly our two boys accompanied from Seattle to SF for $75 each, so it looks like that's what we'll do.