BERLIN—Britain is on course to lose its status as one of Germany’s top 10 trading partners this year for the first time since 1950, as Brexit-related trade barriers drive firms in Europe’s largest economy to look for business elsewhere. Britain left the European Union’s single market at the end of 2020, following more than four years of wrangling over the terms of its divorce during which corporate Germany had already begun to reduce ties with the UK. In the first six months of this year, German imports of British goods sank nearly 11 percent year-on-year to 16.1 billion euros ($19.0 billion), Federal Statistics Office data reviewed by Reuters showed. While German goods exports to Britain rose 2.6 percent to 32.1 billion euros, that could not prevent a decline in bilateral trade, by 2.3 percent to 48.2 billion euros—pushing Britain down to 11th spot from ninth, and from fifth before it …