Kato's new GWR class 800 looked nice. I know they don't run to Portsmouth, but add some batteries and maybe they'd get there.
The Kato supplied decoders, on the other hand, were nowhere as easy to fit as they should have been. The instructions are entirely in Japanese which doesn't help. The motor car decoder needs the body taking apart, then it installs in between two phosphor bronze springs. The two end car decoders should be installable without dismantling, but I could find a way to get it to work. And the pictures in the Japanese instructions didn't tell what orientation they should be.
So dismantle the cars, don't lose the many bits of plastic clip-on bodywork... and it does eventually work. I had to change the direction of one to get the lights correct - edit CV29 to a value of 7.