I'm located in South East London and had mine done just after purchasing my 08 GTi earlier this year, think I paid a smidge under £500.
Local specialists I found when researching the area:
VDS Performance, Redhill
TC Garage, West Sussex
Volks Autos, Sutton
VGS, Keston
AD Autotechnik, Newchapel
I've been using VDS in Redhill without issue. There are closer garages to me on the above list, but VDS is close to a train station which helps when dropping the car off and going to work.