Is it illegal for debt collection agencies to call at 8am ?

Under english law can debt collection agencies legally phone you from 7 am till 10 pm any day.i thought they could only start hounding people between 9am to 9pm. ps i have set my number up as a premium rate so every time they call i get 50p from them and as they call at least 20 times a day in a few months they will have paid their own debt , do i get a prize ?
Answer
They are perfectly within their rights to call at 8 am-the previous occupant to me failed to pay a traffic violation and so the bailiffs were called in-they called at my home at 6.30 am-i had to get my drivers licence and council tax bill to prove i was not the person they were looking for. top marks for the idea though-have a star.