The UK has been accused of reneging on its pledge to nurture a sustainable fishing industry after Brexit by seeking to increase its catch of haddock, hake and monkfish in waters with depleted stocks off the west coast of Scotland.

Demands by British government negotiators for the flexibility to redeploy catch quotas for haddock and other fish from the better-stocked North Sea to waters off the west coast of Scotland are proving contentious during negotiations in Brussels, according to people briefed on the talks.

Conservation groups said the UK government’s approach risked sacrificing sustainability for “short-term profits” as well as undermining its claim that Brexit would enable Britain to take decisions that would “allow marine habitats to thrive”.

The British government is under huge pressure to provide more fish to Scottish fleets after its Brexit trade deal with the EU left the industry accusing UK ministers of betrayal.

British negotiators are looking for flexibility to secure up to 40 per cent of the country’s 27,000-tonne North Sea haddock quota in fishing grounds west of Scotland known as “Area 6a”, where the catch-limit is just 3,800 tonnes, said people familiar with the talks with the EU.

One potential compromise raised in the talks would still lead to a doubling of the haddock caught in the west of Scotland area, added these people.

But in a worst-case scenario, experts calculated the British proposals would lead to a quadrupling of the haddock catch, and would also result in a hit to stocks of cod and whiting because some would be unavoidably snared in boats’ nets.

Using flexibility to shift UK quotas geographically “could possibly increase the fishing pressure heavily”, said an official from one EU member state. Another said cod and whiting stocks would be “decimated”.

The EU and UK have been negotiating for months over fishing levels for more than 100 species that roam between the two sides’ waters. The talks are needed because even though last year’s Brexit trade deal divides up fishing rights, it does not determine overall amounts that can be caught each year.

Last year, in announcing the UK fisheries bill, the then environment secretary Theresa Villiers said the UK would create a “sustainable” fishing industry that would “allow marine habitats to thrive”.

Charles Clover, executive director of Blue Marine Foundation, a conservation lobby group, said demands for flexibility by the UK over where it catches its fish were “the opposite” of the precautionary approach to stocks that was supposed to be guiding the government’s principle.

“The solution is to recover these stocks, not to continue to overfish them,” he added. “The government has, yet again, decided to sacrifice sustainability for short-term profits.”

Andrew Clayton, director for ecosystem conservation and fisheries for the Pew Charitable Trusts, a non-profit organisation, said international scientific advice had advised a zero-catch limit for cod and whiting in the west of Scotland area.

Scottish fishing groups said flexibility over where fish was caught was essential as the industry was left reeling by the impact of Brexit, which has left the sector unable to trade quotas with EU fleets.

Mike Park, chief executive of the Scottish White Fish Producers Association, said while it was important to be “careful” that the flexibility did not pull too much fishing into the west of Scotland area, the boats needed the extra fish.

“We need it more than ever. We need to squeeze every opportunity that we have,” he added. “Because this year we’ll be thousands of tonnes of fish short.”

Elspeth Macdonald, chief executive of the Scottish Fishermen’s Federation, said flexibility was vital to keeping the fleet at sea. “Sustainability has to be looked at in the round, in a social and economic context also,” she added.

The European Commission said the negotiations with the UK were “complex and unprecedented” but the bloc was committed to concluding the talks as soon as possible. It declined to comment further.

The UK Department for Environment, Food and Rural Affairs said it was committed to improving the sustainability of fish stocks within UK waters while delivering stability for the industry.

“Geographical flexibility for stocks of the same species is a sensible fisheries management tool utilised by both the UK and EU,” it added. “This approach does not increase fishing overall.”