The government is under pressure to clarify its policy on border checks at Dover after the transport minister Chris Grayling said there would be none when the UK left the EU.

It comes as Mr Grayling responded to a challenge on how Kent would avoid being gridlocked after Brexit and become the 'Lorry Park of England'.

In an unexpected announcement he said there would be no checks carried out.

He said: “We will maintain a free-flowing border at Dover, we will not impose checks at the port, it is utterly unrealistic to do so. We don't check lorries now, we're not going to be checking lorries in the future."

“We are absolutely clear it cannot happen. We will not in any circumstances create a hard border in Dover that requires us to stop every lorry in the port. It is not possible to do that.”

But MPs and hauliers have both questioned the plans as have opposition county councillors.

The Freight Transport Association (FTA) said Grayling’s promise would “open up the UK’s borders to potential abuse and breaches” and that the UK government would be unable to stop any new checks being imposed on the French side.

James Hookham, FTA deputy chief executive, said the transport secretary “seems to have forgotten that borders have two sides, and the UK cannot dictate what happens to freight when it reaches French customs”.

Delays could have “calamitous knock-on effects to traffic on both sides of the Channel”.

“Mr Grayling cannot speak for the French customs authorities, which will be required by EU law to undertake a percentage of physical checks on cargo such as fresh produce or medicines from a nation outside the EU, which is what the UK will become,” he said.

Meanwhile, a group of MPs said the announcement was extraordinary.

A letter jointly signed by 29 Labour, Lib Dem and Green MPs, said: "It is extraordinary that a government that says it aims to 'take back control' now admits it is not even going to try to control the transfer of goods across our borders, in the event we leave the customs union.”

"This has major implications for our businesses, our infrastructure and our trade."

Opposition Liberal Democrat leader at KCC, Cllr Rob Bird, said: "Mr Grayling is proposing an open border at Dover, allowing anyone and anything to come into the UK. Far from taking back control, the Tories appear to be creating a smugglers charter with the country left undefended against shoddy imports and contraband.

"The only viable way of maintaining a frictionless border at Dover, and in Ireland, is for Britain to be in a Customs Union with the EU.”