LONDON—Trade between the United Kingdom and the European Union was hammered in the first month of their new post-Brexit relationship, with record falls in British exports and imports of goods as COVID-19 restrictions continued on both sides. British goods exports to the EU, excluding non-monetary gold and other precious metals, slumped by 40.7 percent in January compared to December, the Office for National Statistics said on March 13. Imports fell by 28.8 percent—another record. The ONS said the COVID-19 pandemic, which left Britain under lockdown measures in January, made it hard to quantify the Brexit impact from new customs arrangements, and there were changes in the way data was collected too. But there were still signs of a Brexit hit. Trade in chemicals was especially weak, reflecting the winding-down of a rush to stockpile pharmaceuticals ahead of the end of the Brexit transition period, the ONS said. The ONS highlighted …