Unfortunately, as you will probably have gathered if you have been following the recent discussion, it's not quite as simple as "non requirement". In the absence of any explicit 'rules', it is down to the judgement/discretion of an electrician undertaking an EICR as to whether, say, a plastic CU should be coded as C2 or C3 on an EICR - a situation which I don't personally find very satisfactory. I don't think that many of us here feel that it should be given a C2 (even if 'under the stairs), but a few might.
Kind Regards, John
