Banding is the supplement to you salary to reflect the number of antisocial hours you do ie weekends and nights and evenings. They can be 20%, 40%, 50% and very rarely 80%.
So if your basic salary was £30,000 and you were on a 1A banding you would get a 50 supplement making you year earnings £45,000. The banding is rotation specific so might change throughout the year.
You could also be unbanded which would be 9am -5pm, 8am -4pm with no weekends or nights.
If you work in London you get additional "London weighting" which is approx £2000 - £4000" extra. Dont quote me in the exact figures as I have never recieved it!
Hospitals do provide accomodation however in my experience it is not significantly cheaper than private accomodation and often not very nice.
London is the most expensive place in the UK. I live in a much cheaper but of the country however I pay ~ £3000 a year in fuel to travel to and from work. It all depends on what you want and what you are prepared to pay!