I have today found out about the British Gas Energy Trust, which makes grants to help people pay off fuel debts and make a fresh start, they will also sometimes make grants to clear other debts or purchase essential household items. (you don't have to be a British Gas customer)
I have posted on here before about Discretionary Housing Payments. These are available from your local council but you can only get them if you are entitled to Housing Benefit/Council Tax Benefit, and your HB/CTB is less than your rent/Council Tax charge.
There must be other schemes out there - does anyone know of any and would be willing to share?