How would a UK windfall tax on oil and gas profits work?

theguardian.com:

Until this week, the government repeatedly rejected the notion of a windfall tax on oil and gas companies, which have been reaping huge profits from sky-high energy prices.

But the chancellor, Rishi Sunak, hinted at a possible U-turn on Wednesday, telling Mumsnet that such a policy was “never off the table”, and would be looked at if investment by companies in Britain’s energy security failed to materialise.

The idea is that the money raised could be spent on easing the cost of living crisis for those households most under pressure from soaring prices. Sowhat would a windfall tax on oil and gas companies be worth to the Treasury?

Labour has repeatedly argued that a one-off, year-long windfall levy could raise £1.2bn to fund discounts on home energy bills, which are already at a record high of £1,971 for an average dual-fuel tariff, with a further eye-watering rise on the way in October.

The party has proposed levying an extra 10% on the corporation tax paid by oil companies that are active in the North Sea. This would be on top of the 19% rate they pay on their profits.

This would not only effect well-known firms such as BP and Shell but also lesser-known ones such as Harbour Energy – which actually produces more oil from the North Sea than any other extractor, about 163,000 barrels last year.

The sector’s big firms have certainly done extremely well out of the high oil and gas prices that have sent energy bills and the cost of filling up a car to record highs. BP made a profit of £10bn last year, admitting it has “more cash than we know what to do with”. The company was a “cash machine”, its chief executive, Bernard Looney, said around the same time as dismissing calls for a windfall tax.

Shell did even better at £15bn, after