Most of the NATS UK en-route radar are now Mode S. Not so many airport radar yet although Heatrow went Mode S earlier in the year. However some operators had better get their skates on because non-Mode S radar are unlikely to get their licensces renewed after 2012.
In Europe as a whole I think there are over 80 Mode S radar operating now. More info on the EUROCONTROL web site
www.eurocontrol.int