I'm in Wanstead and here the rate is £5.50 - £6 an hour, or £45-£55 a day. But in Ilford it's £2.50 an hour. I do know one childminder who charges £10 an hour but she can't find children to look after so it's not worth over-charging.
In Waltham Forest, depending on where you are, Walthamstow is a bit higher than Leytonstone I think. E17, is that Leytonstone? I rekon it's more around £3.50 - £4. When I started childminding I priced myself too high, because of what other people told me. But our best nursery here (Outstanding ofsted, really popular) charges £55 a day and I cannot see myself as a newly qualified childminder, with no previous childcare experience apart from my own two children, charging more than they do as they have so, so much more experience than I have.
I charge £50 a day, from 8 to 6.30, and I charge for what people use me for. I charge a little bit more than other childminders in my area but don't ask for holiday pay. Deposit is £50. I don't charge more for bank holidays. I haven't had to charge a retainer so far and I don't know what I will charge in that circumstance.
Don't forget practicalities - will you do any of the school runs in your car? Is your car large enough to carry all the children safely? If you walk for the school runs, will you be able to safely walk with 6 children, how many of those will be in a buggy? All the schools in our area start and finish at the same time, so if it's the same for you, you will only be able to cover one school.
You might be tempted to do a school run at lunch time, to cover for children in the nursery, but the problem with that is, especially if you are looking after babies, it is very disruptive. The babies will be spending a lot of time in a buggy during the school runs (one at 9 am, another one at 12, and then at 3:15) it disrupts their sleep, their food, their milk. I have always said no to lunch time pickups it's just too complicated and disruptive for the little ones I look after.