Hi i pay casual workers between £8 and £10 an hour (grounds maint). You will not last long self employed or employing at this price. Charge a fair price and get good customers. The hastle and time taken up runing a business as a self employed person is not worth it at this money.
I would say bare minimum of £10 per hour. Remember that from the hourly rate you weill have to deduct fuel, uniform, acounting feees , tax, advertising costs, vehicle servicing and insurance.
regards Paul