Corporate tax experts have warned that “special pleading” from countries to exclude industries from the G7-backed deal on corporate taxes risks derailing a final accord as technical talks intensify.

The compromise struck at the G7 last weekend papered over the remaining differences between countries over the outline of a deal. However, the UK’s lobbying efforts to exempt financial services has underlined the threat to other parts of the agreement, even if London has valid reasons for its request.

The question of where the largest multinationals pay corporate tax is the most difficult part of the proposal.

Dubbed “pillar one”, it needs a global agreement between countries to allow some of their resident companies’ profits to be transferred to another country, using an agreed formula.

The UK, France, Italy and other countries want to get more tax revenues out of US tech giants and other huge global companies to reflect the business these companies do in their territories.

But the UK is worried that if the financial sector is included it might lose out. It is hoping to exclude financial services, according to officials close to the talks.

Heather Self, UK-based corporate tax partner at accountancy firm Blick Rothenberg, said: “If financial services were included in pillar one, the UK would probably be a net loser because we’re a big exporter of financial services.

“Every country is trying to make sure they come out as a winner but they can’t all be winners, there will be losers too.”

She said she expected to see more “special pleading” from countries concerned about handing over taxing rights to other jurisdictions.

The demand for a financial services carve-out stems from the original OECD plan, which exempted the sector because it “profits from . . . activities that arise in a particular market jurisdiction [and] will generally be taxed in that market location”. Other countries with large financial institutions, such as France, had previously backed such a special arrangement.

For the US, which had blocked pillar one in the OECD negotiations under the Trump administration, even talking about reallocating profits has been difficult. If special exemptions are offered that appear to help other countries but not the US, the deal would have even greater difficulties in Congress than it already faces.

The G7 did agree some special treatment: Amazon’s large and profitable cloud business, Amazon Web Services, will be included even though Amazon itself does not have the requisite 10 per cent profit margin.

Other countries have also broadly agreed with the US position that the original OECD plan was too complicated, with multiple exemptions for sectors and business lines within companies. Instead they agreed to allocate a share of all the profits of just the largest 100 companies in the world.

As the negotiations proceed to the G20 and the OECD in the coming weeks, attempts to modify the careful compromise driven by the Biden administration — such as the UK’s bid on financial services — will need to keep this coalition intact to ensure a final deal.

OECD officials have struck an optimistic tone, suggesting a wider deal will be agreed at the G20 meeting in Venice in July and in their “inclusive framework” talks with over 130 countries later in the year.

“There are a lot of technical issues which the ministers have been discussing, and all the OECD working groups, and we will continue to discuss them,” Olaf Scholz, Germany’s finance minister, said on Wednesday.

But he expressed confidence in the political momentum behind the talks, adding, “with this first public commitment that was made in London, it’s clear that we are moving towards the home straight”.

Efforts to exclude financial services from the G7 deal should not be seen as a concession, according to Richard Milnes, UK banking tax partner at EY. “It is also relevant to note that the concepts of ‘sales’ and ‘margin’ underlying the G7 proposals are not readily applicable in a financial services context,” he said.

But Michael Devereux, professor of business taxation at the University of Oxford’s Saïd Business School, said that although the UK had a strong case on the practical difficulties, its opposition to including the City of London in the deal was also akin to the Americans’ reservations about allowing the rest of the world to tax their tech giants.

Ultimately it will come down to OECD officials to find a formula that makes the deal widely acceptable.

Janet Yellen, US Treasury secretary, highlighted the importance of revenues for the US in a letter she wrote to the Republican senator Mike Crapo, seen by the Financial Times.

The comprehensive scope of the new US proposal for pillar one “will be largely revenue neutral for the United States since we will be on both the receiving and giving end of the proposed profit reallocations”, she said.

Demonstrating that the US gains from this part of the deal will be central to her case that it is in Washington’s interests to agree to it.

Additional reporting by Guy Chazan in Berlin