A no-deal Brexit would spell severe disruption for the UK’s farming and food industries, and hardship for small farmers in particular, the environment secretary, Michael Gove, has said.

Tariffs of as much as 40% would be slapped on British exports and products destined for the EU would be subject to a strict inspection regime, which would cause hold-ups and delays. Small farmers would be most at risk from the effects, Gove told the Oxford Farming Conference, adding that the “real gains” from Brexit, such as leaving the EU’s common agricultural policy, would be at risk in the event of no deal.

“My principal concern is [over the] checking of foods when travelling into the EU, the inspections – all of these things add up,” he said. “While we would adjust to the challenge, we wouldn’t necessarily [be able to] in the short term and farmers, especially small farmers, would face barriers to trade.”

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He strongly backed Theresa May’s proposed deal, which parliament is expected to vote on later this month, though he admitted it was not perfect. “We must not make the perfect the enemy of the good,” he said.

Gove pledged to defend the UK’s high standards for food and animal welfare, which are likely to come under attack in trade negotiations, even though he noted that “not everyone in Whitehall” appreciated their importance. “[There is] consumer resistance to lowering those barriers – the public do feel strongly for retaining food protections and animal welfare protections,” he said, adding that these should be addressed in any trade bills.

Such bills would have to pass the House of Commons, he noted, where MPs would have a say on retaining high standards. “Brexit does not just mean the government taking back control but parliament taking back control.”

Green campaigners warned that a no-deal Brexit would have implications for the UK’s environment beyond farming. Shaun Spiers, chair of the Greener UK coalition, said: “A no-deal Brexit would lead to traffic chaos and air pollution around ports, put at risk many farms and businesses and leave the UK without the means to enforce vital environmental laws. From chemical safety to animal welfare, leaving the EU without a deal would be disastrous for our countryside and the wider environment.”

Gove’s warnings were backed up by Minette Batters, the president of the National Farmers’ Union, who called on the government to give farmers firm guidance on how Brexit would affect them, and put in place plans to ensure the UK’s food supply was secure throughout the process of leaving the EU.

“We are less than 90 days away from Brexit and there is still enormous uncertainty about the future and how domestic food production fits into that,” she said.

Batters stressed the importance of healthy food in people’s lives, saying problems such as obesity were the result of bad diets, rather than bad food. “When I speak to people about food, they do recognise the importance of our sector to our economy, to our environment, and to our food security,” she said. “Food is one of the fundamentals of life. Its importance cannot be overstated. A government that fails to deliver a Brexit that gets this right will fail us all.”

Batters took aim at Gove’s proposals for a new agriculture bill, which many farmers fear overemphasises the importance of safeguards for the environment over food production. She said: “If we ever turn the food production tap off, we will massively struggle to turn it back on again.”

She demanded firmer assurances that the UK would not be flooded with cheap food imports from countries with lower standards than British farmers must adhere to. “If you believe it, write it down,” she challenged Gove.

Tim Breitmeyer, president of the CLA, which represents landowners and rural businesses, said: “As MPs return to parliament next week we urge them to work together to avoid no deal. We agree with the Defra secretary’s analysis that a scenario where the UK leaves without arrangements in place for free and frictionless trade with the EU would have major repercussions for farming, food production and the environment.”

Sue Hayman, the shadow environment secretary, said: “Michael Gove’s speech today was totally meaningless in the face of Liam Fox’s vision of free trade deals that stand to undercut our farming and food standards.

“With only 85 days to go until Brexit, his talk of robotics and artificial intelligence is irrelevant while basic legislation on farming isn’t even in place and there are serious concerns about Defra’s preparedness for a no-deal scenario that would be devastating for farmers.

“Labour is calling on the government to support sustainable food production, provide multi annual payments to farmers and provide a cast iron guarantee that British farming standards will not be undercut by any new trade deals.”