A “large proportion” of traders and businesses will not be ready for new customs and regulatory controls enforced under a no-deal Brexit, a watchdog has warned.
The National Audit Office (NAO), Whitehall’s spending regulator, found the government has not mitigated the “most significant risks” to Britain’s border.
It released the findings as part of a report into the country’s preparedness for a split with the EU on 31 October.
Ministers have insisted government departments are prepared for all outcomes of crunch talks with Brussels.
But with the clock ticking down to exit day, and uncertainty over whether the prime minister will ask for a Brexit delay, questions remain over the contingency plans.
The NAO found progress had been made putting in place the systems, infrastructure and resources required to manage the border if there is a no-deal divorce.
It cautioned “there is still some work to do to finalise arrangements in the short time that remains and bringing all these elements together for the first time in a live environment carries inherent risk”.
The watchdog also said the government’s reasonable worst-case planning assumptions show that the flow of goods across the short Channel crossings could initially be reduced to 45-65%, taking up to 12 months to flow normally.
That was based on the estimate that 30-60% of hauliers travelling to the EU border will have appropriate documentation.
It added there are 150,000 to 250,000 traders, estimated by HM Revenue and Customs, who would need to make a customs declaration for the first time in the event of no-deal.
The NAO said the UK government has announced temporary arrangements for managing trade crossing the land border from Ireland to Northern Ireland
But it branded the proposals “not likely to be sustainable”, adding that there is still uncertainty about border arrangements that the Irish government would introduce.
Gareth Davies, the head of the NAO, said: “Preparing the UK border for EU exit with or without a deal is extremely complex and has required a huge amount of work from many Government departments, agencies and third parties such as traders.
“Despite their efforts, significant risks remain which may have consequences for the public and businesses.”
Downing Street is still hoping for a deal with Brussels, with Mr Johnson expected to update the cabinet and Tory MPs tomorrow afternoon.
Any agreement was expected to be signed off by EU leaders at a summit on Thursday and Friday.
But if that doesn’t happen, an emergency summit could be held next week.
Mr Johnson has said previously that: “If you look at the preparations the UK had made by March 29, we were very far advanced.
“Things then slipped back a bit, but we’re very confident that by 31 October we will be ready and that’s the crucial thing.”