At 5x current most seem to manage around 10ms. Again though, I realise
that this is a feature of the RCD, not a specific requirement of the BS
disconnection times.

It's probably quite difficult to design an RCD that doesn't instantaneously
trip at the next crossing point (or the next crossing point of a particular
polarity). It would need some sort of additional time delay mechanism, like
those intended for TT system incomers.

Christian.