Members of diplomatic missions and consular posts in the UK, and officers, servants or representatives of international organisations should be required to self-isolate or quarantine like everyone else, especially after returning from red list countries.
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Returning diplomats and staff of international organisations are exempt from the quarantine requirements when they return to the UK. However, they aren’t exempt from catching SARS-CoV-2 and bringing back new variants. It’s inequitable and an injustice and could contribute to a third wave in the UK.