If you can get a US mains electricity plug with a USB adapter in it (the thing that should be used for a PT), then that can be used in the UK with a travel plug (multi-adapter type), which you can
buy in the US or UK. There may physically be an issue with a chain of plugs that might need supporting, of course
However if you look at the specification plate on the bottom of your KR8 charger, you will almost certainly find that it accepts 100v to 240v AC, 50-60Hz. This means you can plug it in a US, UK, or EU socket (basically anywhere). Whatever you put into it, you get 4.2v DC out.
All you need then is a travel adapter plug. The US and EU use a two-pin system, in the UK there is a much more robust 3-pin system. An adapter available anywhere fixes that. Adapters can vary, so just check that the two flat pins of the KR8 charger cable fit in the back of the travel adapter, and that it has a UK 3 square pin option on the front.
Sorted.