Britain’s farmers have taken a swipe at Boris Johnson, warning that slashing standards would be “the work of the insane”, after the prime minister attacked resistance to US food as “mumbo jumbo”.

The president of the National Farmers’ Union insisted that nothing is more important than what people will eat after Brexit. “This is not hysteria. This is not mumbo jumbo,” she said.

The comments are a direct response to the prime minister championing US food in a speech earlier this month, when he insisted “pretty well-nourished” Americans disproved “hysterical fears”.

And they come after George Eustice, the environment secretary, hinted that acid-washed chicken – if not chlorine-washed – would be allowed on sale in the UK after its departure from the EU.

“To sign up to a trade deal which results in opening our ports, shelves and fridges to food which would be illegal to produce here would not only be morally bankrupt, it would be the work of the insane,” said Minette Batters, the NFU president.

Speaking to members, she demanded a standards commission to oversee rules on food production after Brexit and for high standards to be guaranteed in law in the Agriculture Bill.

Ms Batters also warned that meat imports washed in “other chemicals” would be as unacceptable as chlorine – a clear reference to lactic acid, following Mr Eustice’s weekend hints.

“What is more important to our economy, our health and our environment than the very food that we eat,” she asked.

Ms Batters also appeared to question the honesty of ministers who have promised to protect standards in the UK, but left doubts about what will be allowed in trade deals.

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“If you raise the bar at home but refuse to legislate in imports then I can only wonder, was the motive ever really about improving global standards in welfare or the environment at all,” she asked.

“This isn’t just about chlorinated chicken. This is about a wider principle.

“We must not tie the hands of British farmers to the highest rung of the standards ladder while waving through food imports which may not even reach the bottom rung.”

Meanwhile, Carolyn Fairbairn, the director-general of the Confederation of British Industry, attacked Mr Johnson for saying he would settle for “Australia-style” trading arrangements, without a formal deal. “We ought to do an awful lot better than that,” she said.

Ms Batters called the Australia-style option “catastrophic” and a “code” for a no-deal Brexit, adding that US officials “mouths dropped” when she brought it up.

On Sunday, Mr Eustice said the government had “no plans” to change the law on chlorinated chicken, but failed to give a categorical assurance.

He then said: “I’m not quite sure why the US would make such demands, because actually chlorine washes on chicken are a very outdated technology and it is not really used by the US anymore anyway.”

The environment secretary then argued that US farmers now used lactic acid washes instead of chlorine.