yeah thats right, as far as i'm aware, the islands they inhabit are more southerly than the areas in australia inhabited by notechis scutatus and have developed the black pigmentation in order to retain heat better in the cooler conditions, the are also larger on avarage as they feed on the relatively large mutton bird chicks
there are two species of notechis, N. Scutatus (pictured in the other thread) and N. Ater, the latter inhabits rocky islands on the southeastern austrailian coast, while scutatus has quite a wide distribution, covering areas like new south wales, queensland and victoria.
unfortunatly the chance of getting either of these in the UK is extremely unlikely.