Shell has called on the government to “provide certainty” over the future of the North Sea after the chancellor confirmed plans to toughen its windfall tax on oil and gas profits.

Rachel Reeves used Labour’s first budget in almost 15 years to raise the headline tax rate of the energy profits levy by three percentage points to 78% until 2030 and close the “loophole” left by the previous government that enabled fossil fuel producers to reduce their taxes through investment allowances.

The government also promised to consult the industry early next year on how its oil and gas tax regime after 2030 could encourage investment in the sector and respond to changes in the oil price.

Shell’s finance chief, Sinead Gorman, said on Thursday: “Elected officials just have to balance budgets in the best way they see fit. We have to look for policies that provide certainty … We invest over the long term.”

She added that after “a number of changes in the fiscal policy” in the past few years, the company continued to “engage constructively with the government on alternative fiscal regimes to support the future of the North Sea and that energy transition in the UK”.

Shell is one of the last remaining of the “oil majors” in the UK’s ageing North Sea basin, where there has been an exodus of large and small oil producers in recent years, in part because of the UK’s tax changes, including the introduction of the energy profits levy by Rishi Sunak in May 2022.

Gorman made the call for fiscal stability as Shell released its latest financial results, which showed the FTSE 100 oil company made better than expected profits of $6bn (£4.6bn) in the July to September quarter despite weaker oil market prices by selling more gas.

Shell’s adjusted earnings for the period slipped from $6.2bn in the same months last year but the profit was still higher than the $5.36bn predicted by industry analysts.

The company announced it would buy another $3.5bn of shares from investors – the 12th consecutive quarter it has showered its investors with buybacks exceeding $3bn.

Shell’s results also revealed a slowdown in its investments in renewable energy, which fell to only 8% of the oil supermajor’s overall spending budget in the latest quarter after the company watered down its carbon emissions targets in March.

Its financial results for July to September revealed that Shell spent $409m in its renewables and energy solutions business, from an overall capital expenditure of almost $5bn.

Mark van Baal, the founder of the activist shareholder group Follow This, said the focus on fossil fuels “jeopardises the future of the company”.

Shell told the Guardian that in addition to investing 8% of its capital expenditure in renewables it was also investing significantly in electric vehicle charging and biofuels through a different business unit, which does not provide a breakdown for these investments. It added that it remained on track to spend between $10bn and $15bn between 2023 and the end of 2025 across its low-carbon energy solutions.

Wael Sawan, Shell’s chief executive, said the company’s “strong results” showed it was continuing to “deliver more value with less emissions”.

Shell has set out plans to grow its gas production over the coming years, in the face of warnings from climate experts that new oil and gas projects are not compatible with limiting global heating to within 2C of preindustrial levels.

The gas business was the largest contributor to better than expected profits after it reported quarterly earnings of $2.9bn, up from $2.5bn in the same months last year.

Aakash Naik, a campaigner at Greenpeace UK, said: “In just the last three months, Shell banked over £4bn and are promising even more to shareholders in buybacks. In the same period, hurricanes and storms supercharged by the burning of fossil fuels have killed thousands, displaced millions and caused billions in damage around the world. The disconnect is startling.”

A Shell spokesperson said: “We agree the world needs urgent climate action. Shell is playing an important role in the energy transition by providing the energy needed today while helping to build the low-carbon energy system of the future. We are investing $10bn-$15bn between 2023 and the end of 2025 in low-carbon energy solutions, making Shell a significant investor in the energy transition.”