The UK government will have to pay up to £30 billion to decarbonise public sector buildings, official figures show.
It is the estimated cost of retrofitting older properties with the latest equipment to help Britain meet its legally binding net zero emissions target by 2050.
The price was revealed to BBC’s Sunday with Laura Kuenssberg show after it made a Freedom of Information request.
The Department for Business, Energy and Industrial Strategy (Beis) said the figure was estimated using "undiscounted 2022 prices", and it was being used as a guide internally to inform decisions and it could change in the future.
The net-zero strategy involves cutting public building greenhouse gas emissions by 75% by 2037.
These include buildings used by the NHS, schools, colleges, the government and local authorities.
Most of the 28.5 million homes and 1.9 million other buildings currently have gas boilers which would need to be switched out, the Climate Change Committee said.
Decarbonising will also involve using solar panels and changing lighting to LED systems.
The committee, which advises the government, said it was important to find the £250bn it would cost to do this over a period of more than 20 years because it accounted for almost a fifth of UK emissions.
David Joffe, who said the current investment was “insufficient”, added: "While the emphasis on public sector leadership is welcome, a larger, firm, multi-year funding settlement is needed beyond 2025 to provide certainty and achieve this decarbonisation target."
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Public sector organisations are eligible for government funding to help cut their carbon emissions and make their buildings more energy efficient, with £1bn already handed out according to figures.
But the government has been accused by MPs of failing to give an effective lead on cutting damaging greenhouse gas emissions.
The Commons Public Accounts Committee said “vague” guidelines and “fragmented” responsibilities within Whitehall meant fewer than half of all government departments were complying with mandatory reporting requirements on emission levels.
The committee said: “We have seen little evidence that public bodies are using the data available to estimate the potential costs of decarbonising the sector, or to identify priorities and develop plans.”
Cabinet minister Michael Gove defended the government’s record on the environment by telling BBC’s Sunday With Laura Kuenssber the UK is the “fastest” decarbonising economy in the G7.
Prime minister Rishi Sunak will be attending the Cop27 climate conference after he reversed a decision to skip it.