Well, Charles will know more so you might be able to find out more information from him, but from the Wizards Play Network event calendar/database, I found the following information about shops which were either in the south(ish) of the country or where I wasn't sure, which ran or at least ordered and planned to run the Game Day, or other non-shop groups:
Burton on Trent - not reported [Spirit Games]
Cardiff - not reported [Cardiff Games]
Chorley - reported [6 players, Chorley Central Library]
Beeston - reported [6 players, Chimera Leisure]
Gravesend - reported [7 players, The 3 Daws pub]
Harlow - reported [14 players, Marquee Models]
London - reported [6 players, Leisure Games]
Oxford - not reported
Reading - reported [? players, Ecclectic Games]
Ripley - reported [14 players, Chimera]
Stoke - reported [8 players, Guys that Game]
Nothing in Bristol, I'm afraid, and while Cardiff Games set up the event they haven't (yet) officially told WotC whether they actually ran it. I don't know if that's any use.