It all depends on location (dictating the wage rate and subsequently the chargeable rate), size of contract (the larger ones attracting a lower margin), and amount and type of capital equipment involved (vacuums to scrubber driers) plus a few other, less significant variables.
Ten years ago the chargeable rate would have been nearer £5-6 per hour as the typical cleaner's wage would have been around £3 per hour.
Nowadays, with the NMW in place, a chargeable rate of £8.50 an hour seems reasonable - but dependant upon the above listed factors.
This is for commercial contracts. Haven't a clue about domestic.
Hope this helps.
Regards
Musicman