The best way to get new customers, by far, is canvassing, try doing the same street, different times in the day, to make sure you get as many customers next to each other as you can.
I asume when you say "i'm taking £4 for a 3 apt £5 for a 4 apt" you mean you are charging £4 for a three bedrrom house, is that right?
I personly charge more than that I'd say £7 - £8 for a three bedroom house, but then prices differ from one place to the next.