Dave wrote:

But if you feed the switched L from the permanent L on the fan the whole
lot is isolated by the 2 pole switch to the permanent L (and N) ...

Sorry, I didn't read your earlier post closely enough to realise you
meant running both light and fan downstream of a DP isolator. That'd be
OK from the safety-isolation point of view, but is borderline as far as
convenience goes (both in real life and in the Regs requirement), as it
means you can't use the bathroom light while servicing the fan: a
particular consideration for 'boxed-in', no-window, loos.

I think we've done this topic to death now...

Stefek