Just a thought, but you might bear in mind that you cannot bring your dogs back into the UK in a private aircraft. They will have to travel with an approved carrier through an approved port of entry or go through the Chunnel.
So, if you're planning to do a lot of flying with your dogs, it might just be less hassle to use the airlines. Alternatively, I think NetJets is an approved carrier. You'll get a lot of airline tickets for £300k, with Netjets your cash won't go quite so far! You pays your money....
Good luck.
MT