Wherever you are in the country £6.50 an hour is a pittance; I wouldnt fart for that. I wonder if your getting confused between what is a good rate of earning and what is the bare minimum.
I used to think ANYTHING was good (maybe I even thought anything is better than nothing).
IMO it isnt what you can get away with but what the market tolerates. I think the way to find this out is to see how many jobs out of the next 20 you price you actually secure. If you secure all 20 then your pricing structure is too low. If you secure 15 its still too low. Secure maybe 10 and your get binned by the others your somewhere near what you need to be.
Another way of looking at it, regarding your £15.00 an hour rate of earning. Lets say on average after weather causes a certain number of hours cancelled work throughout the week, holidays you take, sickness, bank holidays and just days out, that you will work 30 hours a week for 45 weeks a year? That means you'll earn just over £20,000 a year. BEFORE ANY COSTS and associated financial burdens (tax, nat. ins, public liability insurance, materials, vehicle, fuel, vehicle servicing, MOT, upkeep of vehicle............) is there any point in being self-employed if after everything your income is in the same arena as the national average?
Matt