We work inside M25 and charge anything from £12.50 to £18.50 per hour depending on how much we would like the contract (location, hours, storage for equipment etc) however some of our competitors are charging £8 per hour in central london although they are using illegal South American Labour. there is also one company we know that looks to make 75p per hour and goes purely for volume - they make money but its not how I would want to work!
We do only work in communal parts of residential developments though, dont know about EOT or office stuff.