A North Sea oil giant that has been a prominent player in the campaign against the windfall tax has inadvertently shown how generous the UK Government’s treatment of the industry has been as the company faces challenges in its overseas expansion.

Harbour Energy has been vocal in its criticism of the Energy Profits Levy introduced last year, which it warned made the UK a much less attractive place to invest.

The tax was introduced to help fund relief for consumers faced with huge increases in energy bills after oil and gas prices surged amid Russia’s war on Ukraine. North Sea producers such as Harbour made bumper profits following the rise in prices.

Harbour slashed 350 jobs in response to the introduction of the tax and said it would shift investment overseas.

On Thursday the company posted an $8 million (£6.4m) first half loss after tax, against $1bn profit last time. It said the fall into the red reflected the impact of the higher UK tax rate.

However, this seemed to ignore the fact that the profit Harbour made before tax fell by around $1bn, to $0.4bn, following a drop in production. Oil and gas prices fell from the peaks reached last year in the first half amid concerns about the global economic outlook but have remained high by historic standards.

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The tax charge in the accounts fell to $0.4bn from $0.5bn.

In the results announcement Harbour indicated that it received more from the UK Treasury than it paid in taxes during the first half.

“The Group received net tax refunds of $22.7 million in the period … as UK tax refunds from prior years offset the international tax payments made,” said Harbour.

“Ordinarily we would make a final 2022 UK tax instalment payment in January 2023, however as a result of a clarification from the UK Tax Authorities on the payment timing for EPL liabilities for certain subsidiaries we had an overpayment at year-end which was reallocated to shelter this payment.”

The windfall tax was imposed after a long period in which firms benefited from tax breaks introduced by the  UK Government to help the industry cope with the slump that started in 2014. Analysts at the Rystad Energy consultancy said the reforms made the UK regime one of the most supportive in the world.

Harbour’s comments underline the fact the tax charge included in firms’ accounts can be very different from the amount they pay over to the authorities during the period. The accounting provisions can include large elements of deferred tax, which represent estimates of future bills.

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The introduction of the windfall tax has not stopped firms generating huge amounts of cash in the North Sea.

Harbour noted that it generated $1bn cash after tax in the first half leaving it debt free. When the company acquired North Sea heavyweight Premier Oil in 2021 it was left with $2.9bn debts.

Harbour paid out $246m to shareholders in the first half against $140m last time.

Another North Sea firm that has been critical of the windfall tax also showed that business in the area has remained very lucrative even if conditions are not as favourable as they were last year.

Ithaca Energy generated $691m cash from operations in the first half, compared with $989m last time.

 The Israeli-owned firm declared $266m dividends for the first half and reaffirmed the full year target of $400m.

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Ithaca said: “As a direct result of the Energy Profits Levy, investment across our operated and nonoperated portfolio has and will reduce … with production in 2024 expected to be lower than 2023 levels.”

But the company made clear it still hopes to bring big North Sea finds such as Cambo into production. It is focused on finalising plans for the Rosebank field it hopes to develop West of Shetland with Equinor.

Environmental campaigners are bitterly opposed to the Rosebank project, which they reckon could benefit from around £750m tax relief under the investment allowance introduced alongside the Energy Profits Levy.

After buying a stake in the Fotla find east of Aberdeen in July, Ithaca signalled it is in the market for more North Sea deals noting: “We continue to leverage our M&A capabilities evaluating potential inorganic opportunities with the clear intention to increase our production in the medium-term.”

Ithaca is reported to be bidding for a Southern North Sea gas portfolio that Shell is said to have put up for sale with an asking price of more than $500m.

Other bidders include Viaro Energy, which has made clear it is keen to expand its North Sea production operations.

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Ithaca and Viaro declined to comment regarding the Shell portfolio. They are said to face competition from France’s Perenco.

Shell may feel there is limited opportunity to increase the returns generated from mature North Sea assets. In 2017 it sold a $3.8bn North Sea portfolio to Harbour, which was then called Chrysaor.

But Shell still sees exploration potential in the Southern North Sea, in which it recently made a big find with Deltic Energy.

Last week Deltic noted that it has started preparing to drill the Selene exploration well with Shell.

Shell and BP are working on plans to increase production from big fields they developed West of Shetland. BP chief executive Bernard Looney noted this month that the company is working on a five-well programme off Shetland and could apply for more North Sea licences.

Such indications that big players still think there is lots to go for in the North Sea are awkward for the SNP Government.

In the energy strategy released in January the SNP Government recommended a presumption against further exploration for oil and gas in the North Sea. The position may help keep independence-supporting greens onside but has alienated some members of the SNP, who reckon Scotland will need oil and gas for years.

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The value of the industry to Scotland was underlined this month by the latest official analysis of the country’s public finances. The Gers study found the £9.4bn tax revenues generated by the industry helped secure a big reduction in the public spending deficit in Scotland in the latest year.

Those numbers could also cause complications for the Labour party, which has said it will end new North Sea exploration if it wins the next general election.

Such threats could encourage firms to move fast to develop North Sea projects to benefit from the investment allowance.

Harbour has been working to increase output from the Tolmount gas field in the North Sea recently. It expects to start production from the Talbot find next year and is appraising the Leverett gas discovery.

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Meanwhile, not all is going smoothly for Harbour in its bid to accelerate growth overseas following the introduction of the UK windfall tax.

Efforts to develop the Tuna find off Indonesia have been complicated by sanctions imposed on Putin’s Russia. Other investors in Tuna include Russia’s  Zarubezhneft.

Amid reports that it held merger talks with America’s Tallos Energy earlier this year, Harbour appears to have given up on some countries.

This month the company sold its Vietnam business for around £65m.

In its results the company noted: “Since completing the merger with Premier Oil in April 2021, Harbour has exited the Sea Lion development in the Falkland Islands and Brazil exploration licences.”