London Nannys, is 150£ a week a good bargain?

Yes! 150 is a good price for a nanny. This is equivalent to 600 in a month. Some semi skilled workers don't earn such a huge amount in UK.

Sounds like it!

At £25 per day, even as a live in, that would be breaking the minimum wage laws and very probably the working time directives as well. You also by law must offer them a pension.

All you get for £25 a day is an unqualified illegal immigrant with no checkable references.

Or for that money you get an unqualified au pair who is expected to help with child care and household duties (operative word being to "help", not to do it all for you), and £25 a day pocket money while they stay in the UK to learn English is still on the miserly side. If done correctly then you can also expect your male or female au pair to have almost no English when you first meet. So they're not even a real nanny substitute.

That's good if you are living in. I don't have £150 a week pocket money. In London the rent would be more than my salary. With utilities covered for you as well I'd swap places any time.

If you're being offered a nanny for that kind of money, they're thieves casing the joint. If you're planning to offer your services as a nanny for that amount, you really have no clue of what the market is like. That's closer to a daily rate than a weekly one.