To Angelos,
The £520 per month is absolutely fine if they live in and have no bills to pay. It is much more than I have at the end of the month to myself when I have paid mortgage, food bills, fares, etc.
It is pocket money and is used for their own personal shopping (toiletries etc) and hobbies and nights out.
It is more than a student at university has. When I had an au pair they had no bills whatsoever (except mobile phone) and had food provided. They didn't work 12 hours a day though, more like 5 hours and only on 4 days a week plus maybe one night a week babysitting. They only got £70 per week but this was some time ago now as my son is sitting AS levels.
And if they could drive, they got occasional use of a car...