Four hospitals already signed up to deal under which they reduce demand from National Grid by using diesel generators

NHS hospitals are being asked to cut their power demand from the National Grid as part of a government attempt to stave off power blackouts, which the energy watchdog Ofgem warns could arrive as early as 2015.

According to one energy company, four hospitals have already signed up to a deal under which they will reduce demand at peak times by using diesel-fired generators.

KiWi Power, which is a commercial partner of National Grid, says it has started to approach every NHS trust in the country about undertaking similar plans after winning a government contract to encourage power saving.

"We are paying large consumers to reduce their energy consumption. This includes hotel chains, water utilities and NHS hospitals, which can save between £100,000 and £200,000 every year by implementing our demand reduction scheme," said Ziko Abram, KiWi Power's founder and director.

Ofgem warned this week that the UK's buffer of spare electricity would fall from 4% of national supplies to 2% by 2015 and radical measures were needed to increase capacity while cutting demand.

The National Grid, which runs the power wires and gas pipelines, said it would be making payments to encourage energy companies to keep more power stations on standby while paying big businesses to shut off electricity between 4pm and 8pm.

Abram said medical centres were well placed to make savings because they had standby generators available to keep operating theatres and other vital facilities working.

However, the government has failed to convince homeowners that they should adopt energy efficiency measures. Ministers admitted this week that only four households had taken up the Green Deal to make households more energy efficient, although many more had signed on.

Ed Davey, the energy and climate change secretary, has admitted that "without timely action, there would be risks to security of supply". But his department believes the Ofgem calculations slightly overstate the dangers of power shortages.

Davey this week outlined measures including a £10bn guarantee to underwrite new nuclear plants, tax incentives for shale drilling and more long-term help for those building windfarms aimed at strengthening the UK's energy security.

But the shadow energy secretary, Caroline Flint, accused the government on Friday of taking too long to respond to the impending energy shortfall.

"We have known for some time that Britain faces a capacity crunch in the middle of this decade, but the fact the government has taken so long to introduce its energy market reform proposals has hardly helped," she said. "Three years after the government drew up their plans, the energy bill still has not finished going through parliament and lots of important details are unknown. Ministers must clear up this uncertainty as soon as possible so businesses have the confidence to invest in vital new energy infrastructure."

Meanwhile, a second small power company, First Utility, said this week's measures would raise domestic prices and decried the lack of action to shake up the wholesale gas market. "Although improving energy efficiency and providing more generation capacity is important, another option that we would like to see considered is a reform of the way that energy is traded in the wholesale market to lessen the impact on consumers," said Darren Braham, chief financial officer and founder of First Utility.

"Our own analysis shows that the lack of competition in the wholesale energy market, due to the opaque way in which the big six [companies] trade, adds £50 to domestic dual-fuel bills each year – a cost to the country of more than £1.3bn per year. With so little energy for sale on the forward wholesale market, smaller suppliers are penalised, adding to our costs and preventing us from offering even lower prices to consumers."