At the sub-CU end, you mean? If so, then the simplest thing would probably be to have a main switch in it, and connect in the usual way. Although there is a (BS7671) 'requirement' for there to be a single means of isolating the entire installation (which would be the main switch in the 'main' CU), there's nothing to say that one cannot also have a second switch downstream of it (and, indeed, as I said before, that's what I would personally want).
What BS7671 does not want is two CUs, each with their own main switches, fed (presumably via a Henley block) from the meter tails - since there would then be no 'single point of isolation' for the installation.