It would hike the budget to £400m and run the scheme over three rather than two years – as well as providing higher grants – but is not yet thought to have been approved by the Treasury.
Friends of the Earth described the planned programme as “a start”, but one falling far short of what is needed when 29 million UK homes must be upgraded.
“What’s needed are concerted, comprehensive measures, not these half measures,” said climate spokesperson Connor Schwartz, adding: “This barely scratches the surface.
“The pay-off of proper investment is that we will have warm homes that aren’t reliant on polluting gas. This means emissions will reduce significantly and there are plenty of long-term jobs in it.”
Doug Parr, chief scientist at Greenpeace UK, said: “This needs over £4bn during this Parliament so, if true, the debate of £400m or less is that between deeply inadequate and pathetic.”
And Wera Hobhouse, the Liberal Democrat climate change spokesperson, said: “This scheme falls woefully short of the real needs of most families to get their homes to zero carbon in time for this climate emergency.
“Meanwhile, this government is allowing homes to still be built that aren’t zero carbon –which is a scandal. The heating of all our homes needs to be zero carbon in the next 10 years.”
The Clean Heat Grants, to be launched next April, are a small-scale replacement for the ill-fated £1.5bn Green Homes Grant – which was scrapped in March after just six months, because of low take-up.
The plan, first reported by The Times and confirmed to The Independent, must be confirmed well in advance of the climate summit to avoid further criticism.
Heat pumps cut carbon by extracting heat from the ground, water and air, but currently cost about £10,000 compared with only £1,000 for a gas boiler.
Mr Johnson has set a target for 600,000 such pumps to be installed every year by 2028, but it is unclear how that can be achieved – with only about 35,000 installed annually at present.
Replacing gas boilers is seen as essential to the UK’s legal commitment to achieve net zero CO2 emissions by 2050, with home energy use accounting for 15 per cent of greenhouse gas emissions.
However, although experts say new installations must be outlawed no later than 2035, that target may be downgraded to merely an “ambition”, in the delayed strategy next month.
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