I haven't read ANY of this thread and don't know whether OP's still here. Your suppliers won't leave you unsupplied, they'll put in PAYG meters. That's what I've got. It's more expensive, but does mean you can stick a fiver on it as often as possible and this is better than not being able to pay a £250 bill in January.
Depending on what benefits you get, you might get £25 a week when it stays below freezing for the whole week. Mine come up for review at the turn of the year, so I go back onto minimum payments then (thanks, ATOS) so I put as much as possible on the meters before Christmas.
I'm a very un-British cold wuss, so I start 'training' myself in October by turning the heating down by 1 degree every two weeks. By the really cold weather, I should be okay at 17deg during the day and 12 at night. You shouldn't have it below 13 with small children or immune-compromised people, really, at any time.
Leave the heating on and use the programmer to alter the settings to suit your life. Even with up-to-the-minute, efficient boilers, it takes more fuel to heat a house up from freezing than to keep it ticking over (and it feels nicer! Bonus!) If your heating's inefficient, this is even more important.
Insulate. I'm plastering that silver padding stuff (on offer from Wickes) around all the cold spots, and bugger how it looks. If you haven't got double glazing, use that cling-film stuff (also from Wickes) that tightens round the windows with a hairdryer. If you haven't got thick curtains, pad them with blankets (attach them to the back of the curtain with safety pins.)
This house hasn't got proper floors on the ground floor so, last year, I layered blankets and rugs in the living room. I bought them from charity shops.
You will need to use hot water bottles, blankets, duvets, furry socks and layers. Even muffled up, I feel the cold on my face and hands but at 16/17 degrees I'm okay with the layers and socks. Drink hot drinks, it helps.
Everyone's priorities are different but I sacrifice food quality for fuel. In the winter, I live on rice, pasta and lentils made into samey, but satisfying, meals with mince. I use the slow cooker and microwave a lot as my cooker isn't that fuel-efficient, whereas small appliances are.
Run around a lot and keep reminding yourself the summer will come!