No-deal Brexit poses 'significant' border risks: UK audit office

British government efforts to minimise border chaos should the UK leave the EU without a negotiated deal face "significant risks" that are largely outside its control, an audit said Wednesday.

The government's own worst-case scenario assumes trade flows across the Channel slowing by 45 to 65 per cent and taking up to a year to recover in full.

Prime Minister Boris Johnson has created a task force to make sure these do not cause food and medicine shipment disruptions that his government fears could spark riots on the street.

The National Audit Office (NOA) said Wednesday that government departments "have done a great deal to prepare".

But "despite their efforts, significant risks remain which may have consequences for the public and businesses", NOA head Gareth Davies said in the office's updated preparedness report.

"The most significant risks to the smooth operation of the border remain and resolving them is now, to some extent, out of government's control," the report said.

Britain .