The definition of fuel poverty is fairly non-contentious, in that families should not have to spend disproportionate amounts of their resources to adequately heat their homes. The contentious bit is how that is measured. It was done based on some work a very long time ago, in the 1970s, by an academic called Brenda Boardman. She identified that families who spent more than 10% of their income on fuel tended to also be income poor. That has been taken as the definition ever since, although it is reworked as better data comes forth.
However, the measurement isn't based on the actual amount people spend. It's based on how much they would need to spend to adequately heat their homes, given the energy efficiency of their homes and the average fuel prices in the area of the country in which they live. So it's quite a complex calculation. How well it works is a matter of some considerable debate.
It overlaps to a reasonable extent with the poor elderly in terms of income, but it has a much greater rural bias. So in city areas like London, where there are high housing costs, people often have high incomes in order to pay for their housing. But because that's not taken into account in the definition, they appear to not be fuel poor, whereas we know from objective social scientific measures that they often have difficulties heating their homes. So my personal belief is that the idea of fuel poverty is very important, particularly in a cold country.
The current way fuel poverty is measured in the U.K. has caused difficulties in both targeting those in greatest need and in the government meeting those targets. The policies the government is pursuing of identifying vulnerable populations and improving the energy efficiency of their homes is good in terms of also reducing carbon dioxide emissions from people's homes. But the amount of money invested in tackling fuel poverty has been woefully inadequate in trying to eradicate it. The government is not only not going to eradicate it; fuel poverty is likely to increase by 2010.