Kent’s ports and roads could be hit by chronic delays and traffic congestion after Brexit because of the need to introduce new customs checks.

A report says the cost to the UK could be in the region of £1bn a year - and that could be a conservative forecast.

It warns that there could be almost permanent instigation of Operation Stack along the M20 and cites delays in opening new lorry parks as a major factor.

The report comes from a consultancy firm Oxera, which sets out a bleak scenario after Brexit because of the need by customs officials to conduct separate checks.

It has based its findings partly on the length of time it currently takes to carry out checks on non-EU HGVs entering the UK which take an average of 45 minutes.

Under current arrangements agreed when the Single Market was established, no checks are made on goods leaving the UK for the EU and vice versa.

The report suggests that the need for separate checks after Brexit will be severe.

"The Port of Dover has called this scenario ‘Armageddon’ potentially leading to an almost-permanent instigation of Operation Stack - with extensive queues on the M20 and surrounding roads in Kent..." - Oxera report

“Extensive regulation of products, combined with increased levels of enforcement, will lead to a significant increase in the requirements at borders,” it says.

“The Port of Dover has called this scenario ‘Armageddon’ potentially leading to an almost-permanent instigation of Operation Stack—with extensive queues on the M20 and surrounding roads in Kent.”

On the potential costs it says: “We estimate the impact of such a scenario to be at least £1bn per year.

"This is an extremely conservative estimate – it does not account for the economic costs of the uncertainty involved, the extra staff needed for hauliers, ports and customs officials, the congestion associated with calling Operation Stack, the land required for the additional customs checks in the form of lorry parks, or of the wider economic impacts of jobs moving overseas due to uncertainty over the operation of just-in-time logistics.

"The full cost is likely to be much higher.”

Plans for a huge lorry park off the M20 near Folkestone are currently in limbo because of a legal dispute which is scheduled to be heard in December.

Tim Waggott, chief executive of the Port of Dover, said that issues around a new set of customs clearance and border control procedures “are acute”.

“In 2016, almost 2.6m freight units and over 12 million passengers transited the port. Maintaining fluidity at the Dover Straits to protect and promote UK-European land-based trade flows must be one of the key imperatives during the Brexit talks.”