In reply to elsewhere:
> Bathrooms have different zones for mains electrics, over sink and bath at normal height sounds like zone 1 so most risky and more expensive fittings.
> dimmable led transformers are less than 20 quid which sounds cheaper than replacing 12v wiring and fittings with 240v waterproof versions for that.
Thanks for that clear and concise information, just what I needed to know.
For some reason the current MR16 installation has a transformer for each bulb (unlikely to be anything to do with cable run length, it's not a large bathroom). I'll have another look for a dimmable LED transformer that can do all four together.
In reply to comments from others:
There's no shower in the area where the MR16 downlights are.
I am not trying to "get away" with anything, I just wanted to know what the regs were.
I've tried LED MR16s with the current dimmer and transformers and they flicker like the Blackpool illuminations. It was that that led me to discover the complications involved with dimmable LED bulbs. LED bulbs that are a straight swap fitting-wise for incandescents are great, but the retailers really ought to be a bit more up front about the other things that need to be taken in to account if you have a dimmer switch, rather than just labelling LED bulbs as "dimmable" and leaving the customer to find out that they don't work. Turns out that our bathroom dimmer switch (an MK Grid dimmer outside the bathroom door - the other switch is an on-off for the steam light in the shower) is rated down to 40W. Four LED bulbs will only pull 32W. So, new dimmer switch needed, and transformer to match as well.
Smart bulbs don't interest me at all. I can't conceive of any circumstances in which it would be more convenient to control my lights from my mobile phone (which lives in my office when I'm at home, not the sitting room or the bathroom) than from a wall switch. Sorry.
And finally, at the risk of drifting miles off topic: my car has automatic headlights and rain sensing wipers. I find that they work surprisingly well. However, it's trivially easy for me to override them if/when I need to, by adjusting the headlight switch or wiper stalk. But then, my car is seven years old. Do more recent cars not have these kind of simple overrides?