A FLAGSHIP policy designed to help eradicate fuel poverty by boosting the energy efficiency of homes has failed, according to a Glasgow study - with some households left feeling even poorer.

Researchers found "no evidence" that taxpayer-funded housing improvements, such external cladding or fitting new and replacement boilers, had made it easier for the occupants to pay their gas and electricity bills. In one group, householders actually reported struggling to pay their heating bills even more after a central heating system was installed.

The study, based on data from the Glasgow Centre for Population Health, also found that increased fuel poverty was linked to "substantial reductions" in mental wellbeing. This was an "important finding", said researchers, since most studies focus on physical harm such as pneumonia, arthritis and asthma.

However, they added that the group most at risk appeared not to be the elderly population - who receive state handouts including the winter fuel allowance - but lone parents and working age Scots who are in part-time jobs or unemployed.

The Scottish Government has spent more than £650 million since 2009 tackling fuel poverty - defined as a household spending more 10 per cent of its income of income on heating - with a further £500m promised over the next four years.

However, more than a third of Scottish households still classed as fuel poor.

Professor Ade Kearns, an expert in urban studies at Glasgow University who led the study, said it was "an error" to assume that improving the energy efficiency of housing would automatically drive a reduction in fuel poverty.

He said: "They've raised the average efficiency but I think there is a bit of a question as to whether they've raised it sufficiently. There are other studies that say to get a real impact you have to really step up the energy efficiency to a very high level, and Scottish housing is not in the top category yet."

The study compared 1,033 households in deprived communities whose properties had undergone heating and fabric works courtesy of Glasgow Housing Association between 2006 and 2011 against a control group who never received any of the upgrades.

It found that households which received central heating between 2008 and 2011 "were more likely to report an increased frequency of difficulty paying fuel bills than those who did not". The researchers suggest this is because occupants "used their heating differently afterwards" and needed advice on how to use it more efficiently.

Over-65s were also less likely than any other age group after 2008 to report payment difficulties.

Prof Kearns said it suggested that current winter heating benefits were being "poorly targeted".

He said: "There's a misunderstanding that people think of fuel poverty being old people living in cold homes. I'm not saying that doesn't exist but that's not where we're finding the greatest problem.What we found was that it wasn't age that was the biggest factor, but being a lone parent and either being out of work or working part-time. That's a bit of an issue because, of course, the government in the UK and Scotland would say employment is rising - but we know it's rising in the part-time sector, not the full-time sector."

Ultimately the study concluded that the Government's energy efficiency improvements had had a "limited impact upon fuel poverty", which "may be because the energy efficiency of the property is not enhanced sufficiently, or because rising fuel prices outweigh any potential gains".

Kevin Stewart, Minister for Local Government, said the Scottish Government "remains determined to eradicate fuel poverty" and will unveil its new strategy next year, but to date had been hampered by "above-inflation energy price increases that are beyond our control".

He added: “We have also committed to introduce a Warm Homes Bill to help tackle fuel poverty and have a range of schemes in place, including providing bespoke advice to householders through Home Energy Scotland, to support those who may have difficulty paying fuel bills or keeping their home warm.”