there are several reasons why your bill has gone up so much
you could be being charged for the new meter, with a charge being taken off each time you credit your key
your electric charges may have been capped, and the capped period may have ended to the price you pay for your electric has increased - check the price you're charged for each unit and see if you can get a better deal elsewhere
you may have a debt that is being taken off weekly
it does seem a lot when you're hardly using a lot of electrical appliances, but i would trade in the convector heater for an oil filled radiator, as convector heaters are the most expensive to run
i also live in a 3 bed mid terrace, and was at one point paying £150 per month, but changed companies and now pay £95 !! - won't name them in case it's considered defamatory but it's worth shopping around
i actually use 2 storage heaters, also use energy efficient bulbs, but with 3 teenagers in the house, the computers, consoles, tv etc are always on so i am a high user, but my bill is still the same as yours, so there must be a problem somewhere...
also, it may be worth testing your appliances, oven, washing machine etc, just watch the dial going round when they are in use to see if there is a potential problem somewhere, and also write down how many units you use each day, to see if there is a huge spike at a particular time...
hope this helps, good luck, Mandy x