Sean, you're delusional at times. To think that you wouldn't find another customer willing to pay £27 for a 12 weekly clean (£117 per year) within let's say a forty minute drive, assuming the house takes 20 minutes to clean is ridiculous.
My average customer pays over £200 annually for window cleaning. That's not a boast, I'm merely stating what people are prepared to pay for a certain level of service.
This thread seems to have been hijacked somewhat anyway. In response to the original question, you need a grafter, that's prepared to work in all weathers (within reason) that can sustain a good quality clean in volume, all day every day. Chances are he's going to know you're house prices, which is going to get his little brain ticking over, working out how much money he is earning you each day. So unless you pay him well, he'll walk or cheat or try to set up while working for you. Just my opinion