First of all, must point out I haven't read most of the other posts; am just putting in a response to Zealey's OP.
We're in the Home Counties and not in London but even then our nearest nursery charges £890 a child per month. There is a very small discount for siblings but it's not much. Even so, the waiting list is so full that it's not putting any more families on the waiting list. Admittedly, it's one of the best I've heard of, when it comes to staff ratios, quality of food, quality of activities provided, etc.
Have also noted, like one or two others, that Zealey asks how a mum not earning loads affords it - that it is sad that is down to the mum to fork out childcare costs alone. While some may be mums who are single, I too have noticed that many husbands/partners expect the the mum to pay all the childcare costs, while he pays other bills, and often the surplus goes to him rather than the couple. This isn't true for all dads and partners/husbands, of course, but I am amazed that it even happens. Still it does -that's our society I suppose.
Finally, yes, childcare is expensive. But it is an expensive undertaking if the nursery is well run - good staff, adequate numbers of staff with the right skills, maintaining the equipment and venue, keeping things clean, good nutrition, putting on activities that are beneficial and fun for the children, etc etc. Most mums I know who have 3 kids or more no longer send them to nursery and go out to work (admittedly, the oldest will be in primary school already) because of the costs involved - that's just the ones I know, I'm sure there are many who can continue to do so.