Typical electricity prices for a 2-tier tariff (i.e. Economy 7) are, for most of the units you use, around 12p per hour:
http://www.britishgas.co.uk/pdf/Standard%20Ele ctricity%20prices.pdf
That means that 1 hour's use of a 3kW heater will cost you about 36p. If you're using it between 6 & 10pm weekdays, plus, say 8a.m to 10pm at weekends (but with perhaps 6 hours knocked off to go shopping, etc), that's 42 hours per week, which works out at �15.12 per week or �196.56 per quarter. On top of that you've got to add about �25 o,n to take into account the higher charges of the first 125kWh you use. Heating between 10pm and 8a.m is far cheaper, at only about 15p per hour for a 3kW heater.
So, if you were in the flat most evenings and the majority of the weekend, with a 3kW heater turned on full throughout, you could expect a bill of about �225 even if you didn't use the shower and the cooker (or use any overnight heating or use your TV, PC, etc).
So a �200 total bill is probably 'normal' for the colder months of the year. An 'average' household (whatever that is!) now has fuel bills averaging out at around �300 per quarter. However, that's likely to be, perhaps, only �150 to �200 in the warmer months while the colder months might see quarterly bills of �400 to �450. Your �200 bill for an all-electric flat probably isn't out of line with that.
For comparison, I live in a one bedroom 'starter home' (which, despite being on 2 floors, is actually smaller than most one bedroom flats). Apart from the gas cooker, it's all-electric. My only heating is a single fan heater. I'm currently making weekly payments of �18, which equates to �234 per quarter but, due to some stringent economies, I'm hoping that my electricity supplier will soon recognise that I'm going well into credit and reduce those