The British government is warning of 7,000 truck-long queues in Kent in a “reasonable worst case” scenario due to Brexit, a stark assessment of the potential chaos when the U.K. leaves the European Union’s single market and customs union at the end of the year.

In a letter this week to Britain’s border industry, Cabinet Office Minister Michael Gove said the flow of freight between Dover and Calais — a vital trade artery — could be reduced by as much as 80% from normal levels. The government’s worst-case assessment is that as many as 70% of trucks traveling to the EU may not be ready for new border controls, according to the letter.

“The biggest potential cause of disruption are traders not being ready for controls implemented by EU Member States on 1 January 2021,” Gove wrote. “It is essential that traders act now and get ready for new formalities.”

Preparing for customs checks on trade with the EU is one of the biggest logistical challenges facing Boris Johnson’s government. Failure risks major disruption to commerce with the U.K.’s largest trading partner when the Brexit transition period ends on Dec. 31.

The government’s fear is that trucks will be stopped by EU officials for failing to have the correct post-Brexit paperwork, causing supply chain chaos and adding to the economic pain of coronavirus.

Economic Shock

“I would urge the government to get ready and ensure the systems are in place,” Rachel Reeves, Labour’s shadow cabinet office minister, told Bloomberg TV. “A shock to our economy on top of the pandemic and everything we’re going through now would be an awful thing to inflict upon British businesses and European businesses.”

Gove’s letter is the first time a government minister has put their name to the predictions of significant upheaval at the U.K.-EU border in January. Last week, the Guardian newspaper reported on a briefing document from civil servants which forms the basis of Gove’s intervention, warning of long queues and disrupted freight flow.

The government is making “extensive preparations for a wide range of scenarios, including the reasonable worst case. This is not a forecast or prediction of what will happen but rather a stretching scenario,” a Cabinet Office spokesperson said in response to a request for comment.

The British International Freight Association, a major logistics trade group, reacted angrily to Gove’s letter, saying the government is “getting their retaliation in first” and “making villains” of key workers who have been tackling the pandemic’s impact on supply chains.

‘Finger of Blame’

“Don’t start pointing the finger of blame in our direction when you have still to provide all of the tools to do the job,” Robert Keen, BIFA’s director general, said in an emailed statement. “Give our members all the information they need, and systems that actually work, and they will be more than able to do what is necessary.”

Key to the government’s plan to minimize disruption is a new IT system — the Smart Freight Service — which would issue trucks with a permit indicating that they have the right paperwork to enter the EU. Trucks entering Kent without a permit would be fined 300 pounds ($382). However, the government acknowledges the system will still be in testing mode in January, and users risk encountering bugs.

The government is also building facilities to hold trucks with incorrect paperwork, in a bid to minimize traffic on the roads. It recently closed a coronavirus testing center at Ebbsfleet Station in Kent to make way for such a site.

In the letter, Gove said a winter spike in coronavirus may suppress freight demand which could limit the extent of disruption. However, absenteeism among port or border staff and social-distancing measures could have an adverse effect.

The minister also said any restrictions on traffic moving into the EU from the U.K. would impact freight flowing in the other direction too. The U.K. has tried to ease pressure on imports by deciding not to impose customs controls on goods coming from the EU until July 2021.

“We assume both imports and exports could be disrupted to a similar extent,” Gove said in the letter. “Heavy Goods Vehicles (HGVs) that are caught up in congestion in the U.K. will be unable to travel to the EU to export products and/or collect another consignment.”