LONDON—Britain is resisting an EU demand that it grant full diplomatic status to the bloc’s ambassador in London, causing a row between the recently divorced parties that spilled out into the open on Thursday. Britain, an EU member for 46 years, voted to quit in 2016 and completed its tortuous journey out of the bloc on Dec. 31, when Brexit fully took effect. The BBC reported that the Foreign Office was refusing to grant the same diplomatic status and privileges to EU ambassador Joao Vale de Almeida and his team as it gives to envoys of countries, on the basis that the EU is not a nation state. The Foreign Office did not immediately respond to a request for comment. The European Commission, the 27-member bloc’s executive body, said the EU’s 143 delegations around the world had all been granted a status equivalent to that of diplomatic missions of states, …