London, excellent. It is slightly different for London in terms of public transport and ease of getting around and higher desirability for aupairs.
Hmmmm,
Food and toiletries - increased by about £25 per week. But we cook almost all dinners and just increase it by one portion so fairly economical. But aupairs have been known to eat families out of house and home, so depends.
Pay - depends on the hours. I would say £55 to £70 is standard for 25 hours a week + 2 nights babysitting. In London, you can probably get away with paying the lower end of the scale simply because of supply and demand. A lot of aupairs want to be in London so you can pick-and-choose. But of course, living costs are a bit higher.
Travel - I don't pay for a bus pass because it is not necessary for her duties. She does the school run on foot. But will if she needed it. If your aupair needs to use a car (and she shouldn't if you are in London within easy access to bus, tube, train), you should investigate the cost of putting her on the insurance because that is the main expense and related to her age.
Trips out - If on her own time and socialising, her expense out of her pocket money. If we ask her to come out with us, we pay for all food, transport and entrance fees.
Telephone - I provide a mobile phone but cost of using it is her own as it is for her socialising. I bar all international and 090 numbers on our home phone. She can use our home phone to make short domestic calls (eg to arrange to meet another aupair) and for her duties to contact us. If she calls us on her mobile, I will ask her to hang up and call her back to save her the charge.
Computer - we let us use a laptop and of course pay for the broadband. She can also use the laptop to Skype.
TV - she did not require a TV but you might want to consider putting one in her room and the cost of that.
Utilites - If you are not around during the day and she is, be prepared for higher gas and leccy bills. I am not sure, maybe say about £20 a month?
English classes - I definitely won't pay or subsidise private classes. But your aupair should be able to find the community ESOL classes which are either free or subsidised by government to around £400 a year. My last aupair did not require me to subsidise but some families do.
As a ballpark no frills (ie no car or big subsidy for English classes/transport/phone), I would add about £150 to the cost of what you are paying her in pocket money per month.