As we discussed when you first mentioned this, I never really understood this concern, since any currents between the two sets of CPCs would be limited to what the shop's TT electrode could sink - i.e. not very much. As far as I can make out, it would only be an issue at all if the CPCs were joined by something much smaller in CSA than the CPCs in either installation (small enough for 5A or less to be a hazard) - and, if there were such a very thin connection, then that would presumably melt very quickly, essentially acting as a fuse.One "special situation"... The possibility of the CPC derived from the Neutral in my cottage coming iinto contact with the CPC of the TT system in the ajacent shop was considered by the DNO engineers who installed my new supply as a serious hazard as high currents could flow in the CPCs as a result of neutral bounces.
A coming together of the two sets of CPCs simultaneously with a supply neutral fault (I would have thought an extremely improbable combination of events) would, of course, bring the same hazrads resulting from the neutral fault to the shop as existed in your cottage - which may have been a concern, but that's a different matter.
Kind Regards, John