A “temporary solution” to managing cross-Channel traffic in the event of a no-deal Brexit risks turning much of the M20 into a giant lorry park for many years, a report says.

The impact assessment by Dover district council, released under freedom of information, expresses concern over the levels of readiness for the potential situation and states that urgent clarity is needed from the government.

It says: “A 13-mile stretch of the coastbound section of the M20, between junction 8 near Maidstone and junction 9 near Ashford, will be earmarked to hold heavy goods vehicles, in what will effectively become a giant temporary lorry park holding around 2,000 lorries.

“It is likely that a permanent solution will not be in place for many years if enacted through current planning processes and procedures. It will also depend on the post-Brexit customs arrangements reached with the European Union. Therefore, the ‘temporary’ traffic-management system Operation Brock will be in force for some time.”

The document expresses concern at the slow pace of work on Operation Brock, and states “there does not appear to be a plan B”.

More than 10,000 freight vehicles pass through Dover on peak days as it handles one-sixth of the UK’s total trade in goods, with a value of £119bn per year and 99% of the freight moved through the port is intra-EU.

The report says: “The freight vehicles currently only take seconds to clear the port of Dover but if Brexit ends up creating regulatory and tariff barriers between the UK and the EU, it is predicted that there could be gridlock around the town and through to Maidstone and beyond.

“If increased waiting times persisted then perishable goods could be damaged and supply chains interrupted. There is also a potential impact on air quality of any increased traffic queues at border controls.

“Customs checks on imports from outside the common market can take between five minutes to 45 minutes per vehicle. Port officials have warned that increasing the average time it takes to clear customs by as little as two minutes could lead to 17-mile traffic jams.”

The council, which acts as the health authority responsible for food safety checks at Dover and the Channel tunnel, also raised concerns about its powers.

The document asks whether the government fully understands that the port health authority “has powers to examine and detain food, but not to physically stop vehicles in the first place”.

It adds that officials are “in the large ... blind as to what is entering the port”.

The layout of the port is open with no physical boundaries, which means there is nothing to stop vehicles leaving, and the health authority has “inadequate facilities at the port to inspect food or appropriately store food”.

The document states: “We ask that the government fully engages with us to ensure that the food safety function is fully understood and any proposed controls are outlined ... to ensure that they are relevant, workable and logistically feasible bearing in mind the current status.”