Are you for real? How can £6.25 equate to £15.00 an hour self employed? If that were the case then that would mean your expenses are nearly £1600 a month if a full 40 hour week was worked. Your doing something wrong if your expenses are that much!
You are obviously unaware of company national insurance, business (public and employers liability), Corporation tax (if your ltd) accountants fees, banking fees (business accounts charge fees), van insurance, tools, safety gear, training costs, notification costs, gas safe membership. the list goes on, there are a lot of people out there with their hands out, (a lot of them trade "associations"). Then you have the potential for sickness (when you cant bring money in) holiday pay, pension provision etc.
It really annoys me when someone who knows bugger all about running a business bleats when i charge them £35 an hour. They wrongly assume that its going straight into my pocket and I always get the "that's £1400 a week!" comment because they automatically assume that we all have continous work, when in reality our hours are patchy at best. I cant remember the last time I had a full 40 hour week, oh yes I can.. it was when I was an employee and I didn't have all these expenses...
You get my drift?