Tens of thousands of uk businesses are still not prepared for the end of the brexit transition period, civil servants warned on thursday, amid growing fears that the calais-dover crossing will be plunged into chaos next year.

Alex chisholm, permanent secretary of the cabinet office, told mps that he had concerns about the preparedness of companies, with the latest government polling indicating that around one-third of businesses still believed there would be an extension to the transition period.

He told the house of commons public accounts committee: i can understand why they may think that because of the learned behaviour of the previous administration...but there isnt going to be an extension and they really need to be ready before the end of the calendar year.

The brexit transition period ends on december 31.

Meanwhile michael gove, cabinet office minister, announced plans for 10 proposed sites for inland border controls on eu goods from 2021, to take the strain off congested ports.

The sites, which would conduct checks for customs and animal and plant health, include ashford and ebbsfleet in kent, north weald airfield in essex, birmingham, warrington and holyhead. many do not yet have planning permission.

In an update of the government's gb-eu border operating model, mr gove also confirmed that trucks heading for the eu would have to carry a special permit to enter kent.

Those without the correct papers would face a 300 fine. the move is part of an attempt by mr gove to avert massive queues if lorries arrive in dover without the correct paperwork; a government worst-case scenario projected a jam of 7,000 hgvs.

Downing street wants to cut britains reliance on the dover-calais freight route. rachel maclean, transport minister, said: we are working with ports across the country to boost capacity and build a greener way of working so they continue to thrive for decades to come.

But tim reardon, the head of eu exit for the port of dover, said the recent decision by p&o ferries to scrap its hull-zeebrugge route indicated that business was voting with its feet.

The key point for us is that the market is not listening, he said. if businesses wanted to shift their traffic to the north-east or south-west, they could perfectly well do so. the fact that they dont is an indication of what they do and dont want.

Logistics experts, however, said the new border controls that would be introduced after brexit and the potential resulting delays could provoke a shift over time to longer, slower, but more reliable crossings.

Robert keen, director-general of the british international freight association, the industry group, added that longer crossings could also give time to complete complex new paperwork, cut road miles to help hit co2 emissions targets and avoid traffic congestion in south-east england.

Of course we could be wrong and everything will flow freely through dover as it has done for the last 50 years but business will probably redesign processes around longer lead times if they can achieve consistency, he added.

Meanwhile charles michel, president of the european council, who spoke on wednesday with uk prime minister boris johnson, said brexit talks were at a crucial stage, ahead of a leaders summit on october 15-16.

The next days will be very important, he said. this is a challenging situation. we think we need more clarity and we will see if it is possible to make real and concrete progress on the level playing, on the fisheries and on the governance.

Michel martin, the irish prime minister, who spoke with mr johnson on thursday, said the mood appears to have changed in the talks. but he added that the situation was still challenging. there has been more intensified engagement, he told reporters.