Hi Central
As Steve has said, on certain jobs I'm sure £30 per hour can be achieved but I dont know any window cleaners that can get that level consistently day in and day out unless they get involved with some of the high level Reach & Wash equipment.
I'm sure that certain claims about potential earnings assume 3 things:
1) It never rains
2) You never stop to talk to your customers or collect money
3) It doesnt take long to clean the windows and therefor they're not cleaned very well.
HOWEVER, I'm sure someone said in an earlier post that they charged £1.00 a window. I've also read that Terry Burrows can clean 3 windows and wipe the sills in 9.91 seconds. Potentially that's £1089.00 per hour