Hi I used to work for an electriticy company on debt collection on both live and closed accounts so know how the system works.
I am surprised that the meter readings haven't been taken more often, when I worked there about 7 years ago, the meters were read 3 times a year in a city/town and they would estimate the other reading based on those, or if you lived in a rural area they read it twice a year and estimated the other two.
The 2 yearly thing is because they have to do a visual inspection of the meter for any damage or problems.
If they can't read your meter then you should always supply them with a reading if your bill is estimated EVEN if the estimate if pretty spot on -you know it is THEY don't.
So, what you need to work out is what you are actually using so if it is £52 a fortnight then you need to work out what you can afford to pay on top of that.
Trust me when I say they will fit a prepayment meter if you don't come to an agreement BUT they can't set it incredibly high and they DON'T WANT to fit one either as it costs them more money than any other type of customer (direct debit/monthly payer/on receipt of bill payer)
If they argue the rate at which you wish to pay the debt back, then submit (with the help of CAB) an income and expenditure form so they can see you that you do not have the money to pay a high rate. Fortunately CAB and the likes know that the standard income and expenditure form is crap and so have to bump stuff up to cover the little things like buying newspapers and people's birthdays and that unexpected new tyre for your car.
And yes, fags and booze do go on the form, they can't reject it they can just say (trying to remember what our standard line was) something like "we will review this in 6 months and would like to see certain NON ESSENTIALS reduced"
Really hope this helps, stand firm with your offer, say that is all you can afford and they should accept it if it is decent.
Off to pick up my wee one from preschool but will check back later.