Green’s Dictionary of Slang

(UK black) first-rate, excellent.

2005		Ka-Lash-Nek-Off ‘It’s Murda’ 🎵 My nang flow.
2005		Observer Rev. 14 Aug. 7/2: Nang, adj. cool, excellent, as in: ‘Those trainers are nang.’.
2017		Stormzy in Guardian 20 Feb. 🌐 ‘You are sick, you’re nang, you can do this. You’re better than anything anyone’s ever told you that you are’.