The Office of Budget Responsibility said the EU’s decision to impose full customs requirements on UK exports had hit trade since January 1, pulling down Britain’s GDP by 0.5% in the first quarter of the year.
“This reflects both that exports appear to have been hit harder than imports and that the trade disruption will affect UK supply chains.”
It said that would dissipate as firms on both sides of the Channel get used to the new arrangements but that could worsen when the UK follows the EU to impose full customs requirements on imports later this year.
The OBR said its original forecasts had assumed there would be a smooth transition with both sides delaying the imposition of border checks to give traders time to adjust.
That did not happen, disrupting trade and UK supply chains, it said.
Heavy goods vehicles traffic around Dover was 10-15% lower over the second half of January than a year earlier although that had increased in February.
The OBR pointed out that the new health checks at the border due to the new Kent strain of the coronavirus muddied the picture on how much Brexit was to blame.