LONDON — One month after Britain made a New Year split from the European Union’s economic embrace, businesses that once traded freely are getting used to frustrating checks, delays and red tape.

British meat exporters say shipments have rotted in trucks awaiting European health checks. Scottish fishermen have protested at Parliament over the catch they can no longer sell to the continent because of complex new paperwork.

The manufacturers’ organization Make U.K. said this week that 60% of manufacturing companies have experienced “significant disruption” since Jan. 1.

The British government says the troubles are “teething problems,” but companies say they are causing serious pain.

“A teething problem is something that will go away eventually,” said Alan Russell, who runs plant retailer Trees Online.

New customs rules and health checks have prompted him to stop shipping to the EU and to Northern Ireland, which is part of the U.K. but remains in the bloc’s economic orbit because it shares a border with EU-member Ireland.

“It’s 5 or 10% of my business I have just lost overnight,” Russell said. “I’m used to a little bit of unpredictability. But this is without doubt the most severe and unpredictable event that I can’t do anything about.”

Britain left the EU politically a year ago, and quit the bloc’s single market and customs union at the end of 2020. A post-Brexit U.K.-EU trade deal means goods can still move without tariffs or quotas, but businesses face new costs, paperwork and barriers. While many firms prepared as best they could, details of the new arrangements were not nailed down until the trade deal was sealed Dec. 24, just over a week before it took effect.

The British government is accentuating the positive. U.K. supermarkets have not run short of food, in part due to businesses stockpiling against uncertainty caused by Brexit and the coronavirus pandemic. Traffic jams have not piled up at English Channel ports, and the government says its “reasonable worst-case scenario” of 7,000-truck backups is now unlikely.

Cross-Channel traffic is flowing relatively smoothly, with less than 5% of trucks being turned back because drivers lack the correct paperwork, the government says.

Business groups say that’s because some companies are simply staying away. The flow of goods is only about three-quarters of its January 2020 level, and Make U.K. says many firms have “put a hold on importing and exporting from the EU in a hope that things improve.”

U.K. business groups say firms need more support to overcome post-Brexit hurdles. Make U.K. urged the British government and the EU to simplify customs paperwork and to cut “rules of origin” red tape that has left businesses struggling to prove their goods are British and thus eligible for tariff-free trade.

The British government says it is spending millions to help companies adjust. But it also says some of the new trade friction is permanent.

Brexit supporters say any short-term pain will be offset by Britain’s new freedom to set its own economic agenda and strike trade deals around the world.

On Monday, Britain applied to join the Comprehensive and Progressive Trans-Pacific Partnership, a trade bloc of 11 countries including Japan, Singapore, Australia, Canada and Mexico.

But critics note that Britain’s $152 billion in annual trade with the Pacific bloc is a fraction of the $920 billion a year in trade between the U.K. and the EU.