For comparisons sake FF9 & FFX-2 never got more than 200K in the UK, so FF13 has outsold FF9 & FFX-2 there in its first month alone
FF8, FF10, FF12 didn't get over 300K....so they are in the 200K - 299K range....where int hat range specifically we do not know, but it seems FFXIII may outsell FF8, 10, 12 in the UK.
No data for FF7 is present.
Source:
http://www.elspa.com/?i=3942
All hail the KING, Andrespetmonkey