British food sector representatives have urged the government to introduce a transition period if it agrees to realign post-Brexit agriculture rules with the EU.

They warned that aligning regulations overnight would create a “cliff edge” that could cost UK businesses between £500m and £810m a year, because of the divergence in standards since Brexit.

David Bench, chief executive of Croplife, a trade organisation that represents the agrichemical sector, said: “If we do not have a transition period, it would have very damaging consequences.”

The warning comes days after the president of the National Farmers’ Union (NFU) said that British oats used in cereals, snack bars, meatballs and veggie burgers could be rendered unsellable in the EU, because British farmers for the past five years have been allowed to use certain fungicides not yet approved by the EU.

The point of the UK-EU reset is to remove the barriers that have led thousands of businesses to stop exporting to the EU, and to reduce supermarket prices.

The parliamentary trade select committee has said the extra red tape was costing the UK an extra £8.4bn, with goods trade down 18% on five years ago, and food and drink down 24%.

Concerns are being raised as the EU and the UK start technical talks on a new sanitary and phytosanitary (SPS) agreement, one of the targets laid out at the “reset” summit last May between Keir Starmer and the European Commission chief, Ursula von der Leyen.

If an SPS deal entered into force on 1 January 2027, for example, crops grown in 2026 under British rules but still in grain stores in 2027 would be rendered unsellable in the EU, the NFU has said.

Talks between British and EU officials began in London last week with the aim of removing much of the Brexit paperwork for both sides.

One transport chief told the trade select committee Brexit paperwork had been “pure hell”, with one truck held up for as long as 27 days in Calais simply because it did not have the right certificates for a frozen beef cargo.

The Andersons Centre, a consultancy commissioned by Croplife to quantify the cost of realigning with EU rules, said in its report that the UK “has maintained equivalent legal, scientific, and technical standards to the EU, as it adopted EU legislation wholesale following EU exit”.

However, UK and EU decisions on plant protection – including pesticides and herbicides – have diverged, with Britain, for example, allowing four new pesticides and herbicides to be used on farms that are still in the approval process in the EU.

The plea from the industry comes as farming representatives complain of lack of engagement on the topic with the government.

Industry figures fear the government has prioritised secrecy over engagement with sector chiefs.

Bench said: “The impact of a ‘cliff-edge scenario’ on British growers could be devastating. At a time of increasing pressure on farm profitability, this could prove a tipping point for many farmers and growers.”

Croplife and the NFU have called for any realignment to be phased in over at least a year, as happened with Brexit – but ideally over a longer period.