Accessibility (or otherwise) of FCUs

That's its own operational pull switch off/on/power level, rather than a ceiling mounted one in the fixed wiring? 3 mm is the normal contact gap for isolation switches, SFCUs, etc.

Well as you need to fit either a flex outlet or an SFCU that normally incorporate flex outlets I'd do the latter as it kills those two birds with one stone and is less terminals in a high current circuit. Also placed below the heater and accessable kills the emergency switch off bird as well. Dumping the house into darknes in, by definition, an emergency situation does strike me as "ideal"...

You can't put an ordinary switched FCU within reach in a shower room. Personally I wouldn't put a non-waterproof flex outlet where people are likely to touch it or it could get splashed either, but I don't think there is a rule against it. I think the isolation switch the OP already has fulfils the requirements for his heater and a more accessible one is quite unnecessary. It is only for flex protection and maintenance anyway. The pull switch provides safe daily use.

I doubt there is a radiant heater that is "safe" to inside any of the Zones of a bath/shower room. Outside those zones, yes and a SFCU is accpetable there as well.

Yes, it has a switched FCU, but that switched FCU is, as I said, rather inaccessible. It can't be anywhere in the shower room as you can't have such things touchable by wet fingers and bodies.

I guess the FCU could be high up on the wall with the fire. However does it *have* to be there (moderately accessible) as opposed to up in the roof void above (rather inaccessible but OK for maintenance)?

normally

circuit.

AIUI a SFCU is fine anywhere outside the Zones. Of course the room might not be big enough for any of it to be outside the Zones. B-)

I'm sure you're right, but why don't people put ordinary wall-mounted switches in bathrooms (generally)? Maybe there is no great risk of death, but there is a definite risk of a little tingle from touching them with very wet hands.