But the Department for Business, Energy and Industrial Strategy “did not consult meaningfully enough with industry and consumers”, which led to an “overly complex” design with “poor customer experiences” and a “lower uptake” than hoped, the report found.

By the time all remaining vouchers are processed and paid, it will have upgraded only 47,500 of the 600,000 homes it had hoped to reach.

‘It cost the taxpayer £50m just to administer the rushed-through scheme’

Dame Meg Hillier, Labour MP and chair of the Public Accounts Committee, said: “It cost the taxpayer £50 million just to administer the pointlessly rushed-through Green Homes Grant scheme, which delivered a small fraction of its objectives, either in environmental benefits or the promised new jobs.

“We heard it can take 48 months – four years – to train the specialists required to implement key parts of a scheme that was dreamed up to be rolled out in 12 weeks.

“It was never going to work at this time, in this way, and that should have been blindingly obvious to the department. That it was not is a serious worry. I am afraid there is no escaping the conclusion that this scheme was a slam-dunk fail.”

A government spokesperson said: “The Green Homes Grant voucher scheme was designed as a short-term economic stimulus and was delivered during a global pandemic.

“Despite this and other challenges with delivery, all applications have now been processed, with almost 80,000 vouchers having been issued.

“We have taken the experience of the Green Homes Grant into account when designing new measures, with a commitment to go further and faster by investing £6.6 billion in improving the energy efficiency of our buildings, including £1.3 billion this year alone to upgrade up to another 50,000 homes.”