In everyday settings in the UK the self-determination of identity has been taken for granted. In the decennial census and the bureaucratic practices of modern governance, the ascription of ethnicity is in the hands of the subject who is the final arbiter, even if this sometimes breaks down by default. However, for some minority ethnic groups, notably ‘black Africans’, a group ‘created’ by the decennial census, observer-led approaches to determining identity have insinuated themselves into some policy contexts in the UK. The targeting by HIV/AIDS workers of ‘black Africans’ in mundane public settings based on such signalling devices as appearance and language or accent has been endorsed as a modus operandi in preventative care. For around a decade the UK Border Agency has made use of linguistic analysis and other forensic methods to establish the nationality of Somali-origin asylum seekers as against claims from other East Africans. Its latest Human Provenance Pilot Project – the use of isotope analysis and DNA ancestry testing to establish nationality – again places ‘black Africans’ on the front line. These external processes of identification raise important ethical challenges, given the potential for harm when assignment is incorrect.