In its report on ‘Decarbonising heat in homes’, the watchdog warns that “unless the scale and pace of activity significantly increase the Scottish Government’s ambition will not be met”.

Ministers published the Heat in Buildings Strategy in 2021 and officials then spent almost two years building a team to deliver it. Audit Scotland said this delay was due to resource constraints, but added that the Scottish Government would have benefited from addressing its capacity needs sooner. Good progress has been made since 2023, but officials now need to produce a clear action plan, it said.

According to the report, there are significant risks ahead. Success will depend on many pillars, including raising public awareness, providing financial support to homeowners, and securing private finance and supply chain capacity. Much of this work is at an early stage and needs to be advanced before legislation on how homes are heated is passed by the Scottish Parliament.

The Scottish Government has committed £1.8 billion of public money in this parliament to deliver its strategy. It currently estimates it could cost the public sector, businesses, and households £33 billion in total. But the final cost will be influenced by several factors, including inflation, the price of heating systems and the impact of new legislation.

Stephen Boyle, auditor general for Scotland, said: “Getting most households in Scotland to change to low carbon heating systems is a huge challenge. It is complex and relies upon a range of stakeholders and partners, including the public, the private sector and the UK Government.

“The Scottish Government now needs to carefully consider how to maximise its public spending and set out a clear delivery plan. It also needs to help the private sector to roll out funding deals that will support people to change how they heat their homes.”

Responding to the report, Gillian Campbell from the Existing Homes Alliance said: “While the report recognises that progress is being made, much of this work is at an early stage. With nearly £600m of the Heat in Buildings budget currently unallocated, the Scottish Government must invest in scaling up the advice and support available so people are helped to upgrade their homes, cutting bills and cutting greenhouse gas emissions.”

Fabrice Leveque, energy policy manager at WWF Scotland, said: “The Scottish Government has rightly prioritised the heat transition, but this report is a wakeup call, showing that there is no time to waste if we’re serious about delivering lower carbon, lower cost heating for households and businesses.

“That’s why we need to see a Heat in Buildings Bill this summer, to give businesses the confidence to invest, and tradespeople develop the right skills to deliver the transition away from fossil fuel heating.

“The sooner we begin this transition, the sooner we can see homeowners enjoy lower energy bills and warmer homes, and Scotland can play its role in tackling climate change by ending a key source of our emissions.”

Scottish Labour net zero spokesperson Sarah Boyack added: “With energy bills soaring and fuel poverty rife, it is more urgent than ever that the SNP sets out a clear plan to upgrade homes and modernise heating systems.

“Labour’s plans will insulate up to 1.4 million homes across Scotland, cutting household bills and emissions and creating jobs in our communities.

“Warm words don’t heat homes – the SNP must listen to Audit Scotland’s stark warning and set out a real plan to deliver on their promises.”