So I'm with everyone else thinking that your energy bill is INSANE. I have a 4-bed end of terrace and I pay £120/month for gas+electric which includes charging my electric car.
Last I checked the split was roughly in favour of electric: around £70 electric and £50 gas. I am by no means frugal- the heating comes on at 21 degrees at 5 in the morning and stays at that point all day until 8pm when it drops to 19, and down to 10 degrees at 11pm.
There are a few things that need checking- first of all your old radiators. How old? Secondly, have you had a power flush of your system? Have you insulated (lagged) your central heating pipes that are outside the heat envelope of your home (under the floor or outside the house if they travel that way?). How insulated?
That is an insane heating bill. If I am presuming that your electric use is not over represented then at most £100/month is electric. So £560/month on gas.
Gas unit price is 0.04 (or was last year). So you were using approx 14,000kwh of gas per month. If your boiler is big, say a 45kw boiler, then that is equal to your boiler being on full blast, absolutely full tilt for 10 hours per day every single day of the year including summer. Presumably your usage profile is like everyone else so it's more like not at all in summer, a little in autumn and spring and a lot in winter. Which is the equivalent of 20 odd hours full tilt every day during winter.
Your house must have been a FURNACE.
If it wasn't- if it was just something like a fairly standard 20-22 degrees, then there is something seriously wrong with your heating or gas setup. If you had a bill of thousands on top of £660/month then there is something seriously fucked up. I'm not quite sure how you could even actually consume that much gas.