The Government announced the grants as it confirmed a target for all new heating system installations to be low carbon by 2035, but insisted families are not going to be forced to remove their existing fossil fuel boilers.
Switching to low carbon heating in the coming years will cut emissions, and reduce the UK’s dependency on fossil fuels and exposure to global price spikes in gas, ministers said.
The Prime Minister said: “While we’re going to have to make some pretty major changes to the way we heat our homes, the Greenshirts of the Boiler Police are not going to kick in your door with their sandal-clad feet and seize, at carrot-point, your trusty old combi.”
Responding to the announcement, the Scottish Government insisted it was already going further.
A spokesperson said: "We are wholly committed to becoming a net zero nation by 2045 and, in line with this, to supporting the rapid decarbonisation of emissions from our homes and buildings.
"The Scottish Government already offer a comprehensive support package for domestic and small scale non-domestic heat and energy efficiency measures through our Home Energy Scotland and Energy Efficiency Business Support services.
"Our existing funding scheme for zero emission heating systems, including heat pumps, already goes beyond the support offered by the UK Government' s Clean Heat Grant, with grant funding of up to £7,500 per household, in addition to a further £6,000 of grant for energy efficiency improvements as part of the Home Energy Scotland Loan.
"The Energy Efficiency Business Support Service SME Loan also offers grant support for SMEs.”
The plans form part of the UK Government’s Heat and Building Strategy, which misters say “will support up to 440,000 jobs across sectors and across all parts of the UK in 2030.”
Energy minister Greg Hands said: “This is not just an environmental transition, it represents an important economic change too.”
He added: “We will fully embrace this new green industrial revolution helping the UK to level up as we build back better and get to the front of the global race to go green.
“We need to capitalise on this to ensure British industries and workers benefit. I can therefore announce that the strategy will support up to 440,000 jobs across sectors and across all parts of the UK in 2030.”
But experts and environmental groups warned the £450 million three-year pot to switch from boilers would only pay for 30,000 heat pumps a year, a fraction of what is needed to meet Government targets.
Shadow energy secretary Ed Miliband said: “The plan falls short on delivery, and while there is modest short-term investment, there is nothing like the commitment we believe is required. And we know why.
“The Chancellor’s fingerprints are all over these documents and not in a good way. So we’ve waited months for the heat and buildings strategy – it is a massive letdown.
"My fear is this plan will not deliver the fair, prosperous transition we need equal to the scale of the emergency we face.”