Trojan Airsoft is one I would fully recommend, and I know a few other people who have been and can only say the same.
Airsoft Forums UK
Cheeky vimto
I did Trojan indoor CQB about 2 years ago. I think it was fairly new then? I weren't too keen on it, maybe it's changed?
Cheeky vimto
I'm pretty sure the hive is closed now.
SWAT - now outdoor
F&O The Hive - CQB
Trojan Airsoft - they have one of each i believe