if you are in Scotland Scottish Hydro will remove the prepayment meter and set you on a quarterly bill for no charge and no credit check
There is a big difference between pre-paids and 'normal' bills.
Also if you are on benefits (ESA/JSA/DLA/Income Support/Pension) you can make an agreement with the power company to take a set amount from your benefit per week to cover usage and you are not charged anymore than the set amount.
I am charged £10.55 a week, this is deducted straight from my benefit payment (I'm on ESA at present due to a health condition)
The amount used still accrues and if/when you are back in work/come into money the bill you have is still due however, i started with a bill of £515 and now my outstanding is £215 which means, I think, my payments have reduced the outstanding bill.
I'm not entirely sure but I'm guessing, and only guessing here, that if you are successful in getting the power companies to take a set amount from your benefits they sort of stop charging you silly £'s a month (perhaps because they realise you can't afford it and repay it)
It took me a lot of time to discover this was available for people on low incomes, weeks of phone calls and I got angry with them, I cried with them (which I was not proud of) but eventually I found the correct department in the power company and the direct deduction from my benefit was agreed
This should be more highly published as very few people know about it
I'm happy to pass on the details, I'm with Scottish Power and can provide contact details for that company,
I've been lead to understand every power company can arrange this, however I only have experience with Scottish Power so can not vouch for other power company
Apologies for the long post but I just want to share my experience as it might help others who are having to choose between using the electricity to cook a meal, have a wash, or keep warm.
It's disgusting people can't afford to cook, wash or heat their homes in GREAT BRITAIN .........we give money to charities in Africa for this exact same thing 
Sorry for the long post and getting on my high horse but if this can help just one person or one family that would be good