I live with my partner in an old fashioned ground floor flat with no cavity wall insulation, and only part double glazed, the only gas appliances we have are a boiler for hot water (use hot water on average an hour a day) plus 3 radiators, which in winter we do switch on a lot. My supplier just tried to increase our monthly DD again, but I have still kept it down to £26 a month, based on previous consumption. So we are on about £300 per year for a really energy inefficient flat.
Your landlord is definitely pulling a fast one. If you are living in a house where the flats and bedsits are self contained (i.e not living in a shared house with all amenities shared between occupants), then I really think you should all be on separate metered supplies! If this isn't possible due to a shared supply to the building, then try to find out who the supplier is, get a year's worth of consumption data from them, try to have a look at the meter if possible and monitor the readings, and get together with your fellow tenants to challenge what you're being charged.
I'm afraid this sounds like the modern equivalent of the old landlord scam of fiddling the meter. Back in the days of putting coins in, they would up the tariff rate on the meter to make tenants pump in more 50p's, then skim off the profit, these days, they include utilities in the rent and then scam it that way.
PS turn off the radiators in the entrance hall if not needed, and tell him you're not paying for them!
good luck :)