Jesus, those costs are sky high!!
We pay 11p per unit any time of the day on a non economy 7 system with Scottish Power. Boiler heats as and when the water drops below 60 degrees (no control over it other than turning it off), all our heaters are 1.5kW wall panel heaters that we turn on as needed and probably 2 or 3 of them get used for a few hours each night atm.
I mean, if you take one of the heaters at 1.5kW, thats 1.5 units per hour its on full whack (which they never are as they have a thermostat so in reality they are heating for about 50% of the time they ar switched on). So if we pay 11p pepr unit thats 16.5p per hour of usage, £27.72 per week, £110.88 per month (assuming 4 weeks in a month).
So really, unless you have like 10 of the things on for hours and hours at a time, with an economy 7 boiler you would have to be working REALLY hard to use that much electricity (though your tarriffs are very high!)
I'd get it questioned, either the meter is faulty or they haven't taken the readings you submitted when you moved in, into account, and someone has used loads of units in between the previous tenants moving out, and you moving in.