Almost two-thirds of the £150 million boiler upgrade scheme (BUS) funding risks being lost at the end of this month.

Ofgem’s latest figures on the BUS reveals that more than £95.8 million remains in the pot, with just weeks left for it to be spent.

The remaining amount far outweighs the £43.6 million of BUS vouchers redeemed since the scheme was established in April last year.

Last month, energy minister Lord Callanan admitted that any money left in the BUS fund at the end of March will be returned to government under Treasury rules.

A separate £300 million will then be released on 1 April as part of the second phase of the scheme and will fund boiler upgrades for two years.

Under the scheme, which is set to run from 2022 to 2025, households can access £5,000 grants to help cover the cost of replacing gas boilers with low-carbon alternatives, principally heat pumps.

As of February 28, 10,756 vouchers had been issued with a total value of £54.1 million. Of those, 8,689 vouchers worth £43.6 million had been redeemed.

The BUS has been plagued by setting up problems, principally the delayed launch of the full online portal for submitting applications, which only went live at the end of November.

Mike Foster, chief executive of the Energy and Utilities Alliance, the trade body for boiler manufacturers and gas companies, previously called for the scheme to be scrapped with money reallocated to other energy efficiency scheme.

“The Boiler Upgrade Scheme is failing,” he said. “The latest figures suggest that at best only 40% of the cash allocated to the scheme will be spent. The rest goes back to the Treasury. The scheme is flawed, rewarding those with large sums of cash at their disposal with a £5,000 bung at a time when millions of households simply can’t afford to heat their homes and they face bills rising a further 20% in April.

“The BUS should be scrapped and the cash allocated to invest in energy efficiency such as loft insulation, helping the least well off afford to keep warm. It is obscene to use taxpayers’ money to subsidise a purchase of a heat pump for people who would probably have bought one anyway.”