Kane_richards:
I tend to agree with the last poster that the current monthly amount does seem a bit high, though equally the flat could be badly insulated and you like to be warm.
The actual number (now) is really not that relevant. Ignore it for the moment. Go to your preferred Consumer Focus accredited comparison site and do a comparison. Use "average annual consumption" figures. You will get a list of tariffs in increasing price order. That's it. Choose you supplier and tariff. Note that the cost per year is only valid for the "average consumption" you entered.
How much energy you are using is a different question and can only be answered by monitoring your meters. Get a handle on your consumption by reading the meters daily for a week, then weekly for a month. After that keep on top of any estimated bills by submitting actual readings. Obviously its a cold time of year and your consumption, particularly gas, will be high.
Suppliers monitor account balances with the objective of achieving a zero account balance by the next review date (usually annual but NPower is bi-annual). By all accounts some suppliers do this better than others.
BTW I don't understand "the previous owner of the property I'm now in was with EDF Energy so to pay the outstanding balance with them I signed up for monthly direct debit". You do not have to pay a previous occupiers "outstanding balance". Is that a misunderstanding? I hope you supplied meter readings when you first occupied the property.