My question is, do you know anyone in Europe that would be willing to care for your pet while you are in the UK (that is, if you can't find someone in the US to care for him)? What about France? It is quite close.
I am going through a similar situation myself and really feel for you. I am planning on taking both of my dogs to Sweden with my DH and I when we move. Sweden has a 120 day waiting period after the rabies injection (and after the special microchip) and then you can only send the blood sample to be tested for FAVN to Kansas State University. We have done that, but there is a five week waiting period and we still don't know the results but have to book our tickets soon!
Very stressful and sad.
Good news - in January 2012 there will be no more requirement for FAVN testing at least so that will be a huge relief for many travellers. Too bad it isn't for January 2011 as it would help us all out on here!
My back-up plan if the dogs don't pass their tests: move to Denmark. No rabies antibodies testing there. Leaving them in Canada is a no-go as all my family live in "pet free" condos/apartments. Plus, they love them lots but nobody could love my doggies like I do!
Good luck, let me know if I can help in any way, shape or form. I really feel for you - the rules are confusing and excessive.