Tory ministers are accused of letting oil and gas firms “off the hook” after a windfall tax raised £2.7billion less than expected.
Official figures show the levy brought in £4.4billion in the past year, way below the £7.2billion the government had forecast.
The Liberal Democrats demanded ministers bring in a tougher windfall tax and scrap loopholes.
The “investment allowance” allows oil and gas companies to offset taxes against new investment in fossil fuel extraction.
Treasury spokeswoman Sarah Olney said: “This black hole shows the Conservative government’s botched windfall tax isn’t raising anywhere near the money they claimed it would.
“Rishi Sunak is letting oil and gas companies off the hook, while hiking taxes and energy bills for ordinary families struggling to get by.
“It shows the Conservatives are so out of touch they may as well be living on another planet.
Liberal Democrats want to see a proper windfall tax on oil and gas giants, which could fund a £400 cut to the average household’s energy bills this year.”
The Energy Profits Levy was introduced in May 2022 as prices soared following the Russian invasion of Ukraine.
The 25% tax was applied to profits made from extracting UK oil and gas, but not from other activities such as refining oil and selling petrol and diesel at forecourts.
In the Autumn Statement in November, Chancellor Jeremy Hunt announced the rate would be increased to 35% from January with the levy extended until March 2028.
Treasury documents published at the time forecast the windfall tax would bring in a total of £7.2billion in the 12 months to the end of March.
But figures published by the Office for National Statistics earlier this week show it has actually raised £4.4billion.
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