UCAP run a pretty good skirmish day and have a milsim coming up on the 11th of july weekend. Its at the Sandpit, next to Bluewater in Kent.
Stirling use their sites.
Gunman have a fantastic reputation and loads of sites, their regular weekends are pretty much along the milsim line, there is limited ammo etc. They also do stuff that is far more about getting into a character. They do a series called flying lead, based on a wild west town, players build up their characters over games have "jobs" etc. They do WWII as well and that is just the tip of the iceberg.
It really depends on what you are after, most cut out the standing on guard duty bit out although from what I have heard sometimes Stirling do do that stuff.
