Hostel in central London (good for airport commute) from £10 per night.

If you don't like sharing rooms its not for you. But I know myself I like stopping in London if I get the chance and at around £10 - £15 per night including breakfast in the capital you can't really go wrong.

http://www.laterooms.com/en/hotel-reservations/249533_journeys-greenwich-hostel-london.aspx