You will have to check with the UK X10 supplier to see if they have ActivePhone for England. The US version does not work outside of the US or Canada.
The US version of the software WILL work outside the US and Canada, but the hardware is different (and the part numbers of the modules are different). as long as you are using the correct modules for your country, the US version of AHP should be able to control them via the correct UK version of the CM15.
I don't know if the plugins for the US version will work with the UK version of the software, though.