They have been called “negawatts” — the vast amounts of electricity and heat wasted around the world every day from homes, businesses and appliances as well as ageing power plants.

Energy efficiency may sound unglamorous set against plans for shimmering new solar power plants or giant offshore wind farms.

But it is hard to dispute Professor Chu’s assertion that it represents the easiest route to large reductions in global carbon dioxide emissions.

The US Government claims that better buildings alone could cut US energy use by a third. Modest improvements to existing buildings would allow cuts of 10 per cent.

About half the energy produced by burning coal or gas at a British power station is lost immediately as heat. More goes in transmission to consumers and more still at household level with inefficient use of appliances, lights and devices needlessly left on.

A true revolution would affect almost every facet of modern life, but the technology exists. Finland has heat and power plants where more than 90 per cent of raw energy produced is delivered. In Italy, 30 million “smart meters” — encouraging efficiency — sit on walls of homes and businesses.

But the shift takes time and can be expensive. Britain faces real challenges because of the age of its housing stock. The Government talks of energy efficiency as a key plank in its wider aim of slashing emissions by 34 per cent by 2020, but concrete achievements are rare.

Stop-start funding has hit the Low Carbon Building Programme, while the carbon emissions reduction target has been open to abuse with many power companies finding the cheapest way to meet their obligations is to distribute vast numbers of low-energy light bulbs – with no need to show how many are actually used.

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