For at least a year after a no-deal Brexit, most shipments of goods would be allowed to pass through UK ports and the Channel Tunnel before customs officials had been informed of their arrival and before any duty was paid.
Importers would have to tell HM Revenue and Customs “as soon as possible” after the goods’ arrival in the UK and no later than the end of the next working day.
Campaigners for a second Brexit referendum claimed the plan amounted to “waving things through irrespective of our safety”.
But HMRC sources insisted security checks on controlled goods would continue unchanged and officers would continue to target suspect cargo on the basis of intelligence and risk assessments.
Under the Transitional Simplified Procedures, registered businesses would be able to transport goods from the EU into the UK without making a full customs declaration at the border and would be able to postpone paying import duties until the month after import.
HMRC has written to 145,000 businesses that trade with the EU to inform them of action they need to take to operate under the arrangements.
Financial Secretary to the Treasury Mel Stride said: “Leaving the EU with a deal remains the Government’s top priority. This has not changed.
“However, a responsible government must plan for every eventuality, including a no-deal scenario. Businesses and citizens should ensure they are similarly prepared for leaving the EU.”
Mr Stride said the new procedures would “ease the transition, especially for businesses new to the rules associated with importing”.
It is anticipated that the TSP arrangements would be in place for more than a year after a no-deal Brexit, with a review conducted three to six months after their introduction on March 29
Labour MP Geraint Davies, a supporter of the Best for Britain campaign for a second referendum, said: “They said we would take back control of our borders but now the plan is to wave things through irrespective of our safety.
“We’ll have no idea what is coming into our ports.”