For me cargo was the only option. I had a friend who works for an animal rescue operation and she helped me with some of the ins and outs/dos and don'ts for shipping animals in cargo. As I was moving to the UK, there wasn't another option for them.
As for getting another microchip in England - why bother at that point. Wouldn't the point of getting another microchip be so that you didn't have rent a scanner to take over there?