Multi-national. It's perfectly acceptably to have more than one nationality - IF those countries have provision for this (such as dual citizenship agreements) and you meet the specific requirements.
Even if someone doesn't, then individuals can still identify with multiple cultures (such as the country of their birth or their parents' origin), but they can have NATIONALITY only for those where they have (or retain) citizenship - and by implication eligibility for a passport.
If the alleged felon with the dark skin holds a British passport, then he is a British national.