I don't understand why people are quoting "salary" and "minimum wage" on this thread. These things apply to nannies because they are employees. Childminders, on the other hand, are business owners.
If a childminder is making less money than another childminder in his/her area, perhaps he/she should look into why. I used to have a childminder in Epsom who charges £5/hour and is always full. She works full days, and I once calculated the sums based on the number children, number of hours, and the rate of pay and almost fell off my chair when I realised she takes in about £4000 / month. Everyone pays her in cash, and she reports "some" of it. I don't know how much, but she is no doubt making a healthy income.
I will also say that she is a fantastic childminder. We love her and miss her dearly (we left because we moved and because I wanted a live-in nanny to accommodate my work schedule).
So, I know that Surrey is more expensive, but I still suprised that some of you only charge £2.?? an hour. I wonder if there might be some more services you could offer to your parents (like a friendly newsletter to keep them informed of what their kids are doing, or possibly give them daily reports of progress???)
It seems to me, though, that as a business owner it is up to you to sort out how to market and sell your services for a reasonable profit. Whether that is more kids or additional services, I don't know. But, I do think that parents will pay a bit more for a "better" childminder. For example, the reason I paid £5/hour was because I was working long hours and showing up on time was often something I could not promise. So, we had a deal (up front) that any additional hours would be charged at straight time and at the end of the week she would add up the number of hours I had gone over in total that week and I would settle the extra fees each Friday.