Somewhere in my searching on EITS, believe that, at some time when Colin Firth was supposedly in the cast of the film, his role was to be a British official and the cast was an ensemble one. So, obviously, if as I believe, JN has been cast in the CF role, he, also, will be a British official.

If you notice, Alan Rickman has not been mentioned as being in Cape Town, so, perhaps both AR and JN will be filming their scenes in the UK in a studio setting.