There is only one English installation CD for XP, for both the US and the UK.
I don't believe that anybody knows exactly what is the difference between (1) specifying either US or UK during the installation of Windows, and (2) changing the locale after Windows was installed. It's most likely that the two are totally equivalent, but there's always a small niggling doubt somewhere.
To be 100% sure of having a clean XP installation the same as done in the UK, I would advice to create a virtual machine containing a new XP installation done with the UK flavor (and especially the UK keyboard). Such an installation is guaranteed not to have any US residues.