In-line fuse holders - do they meet the regs?

I'd say anything connected to a ring needs an FCU. Run it from the lighting circuit?

You may be correct (I don't know) but the purpose of the fuse is to protect the (fixed) wiring between the device and the ring so what's the difference between an in-line fuse inside a back box and a fuse in a faceplate? I can accept that it would be useful to have a label saying "fuse inside", but I can't find anything in the regs; hence the question.

The lighting circuits are too far away.

I'm not certifiable (yet) but have a couple of questions and comments.

First, what if anything do the manufacturer's instructions require?

Second, I am not clear what - if any - means of local switching and isolation you end up with. An unswitched FCU to BS 1363-4 counts (Table 537.4 in the regs): you can remove the fuse without risk to life and limb. But what you propose ain't to BS 1363-4 and AFAICS could only remove the fuse by opening up the back box. So I think that's a problem.

Has anyone ever opened up a wall wart recently? Time was when there used to be a fuse or at the very least a temp sensor in the transformer to stop it all bursting into flames. Most of the little switch mode ones have nothing at all. I think if anything goes short the main trip on the ring is the only way to cut the power. They have been known to melt or catch fire. Surely a little in line wire ended fuse cannot be that expensive to fit rather than a bit of flexible wire as they use now. Brian

Perhaps I'm heading in the "certifiable" direction ;-)

There's nothing about protection

You may be right but the fuse would only need replacing if the PSU fails, and that is in the back box. All connections would be insulated and I found an inline fuseholder with appropriate protections (although I can't find it now) so I think it meets the intent, but maybe not the letter, of the requirements.

Many of the cheapo PSUs just use a low value resistor as the first component from the live terminal as a fuse now...

Following that thought chain, the fuse could be non-replaceable and considered part of the PSU. So something like

You ought to be able to isolate the PSU, ideally with a DPST swtich so I don't see why you are so against a switched FCU.

It doesn't have to be co-located with the PSU as long as it's still accessible.

Yes, I was trying to reduce "stuff" on the wall. In fact, because the controller is wifi-connected, I would probably get better range if the controller was remote from the PSU and any other metalwork. More thought required

If the manufacturer lays down no requirements and your only concern is to protect the cable (ie no local switching or isolation required) then ISTM you could just extend the ring final circuit to the PSU and avoid the need for a fuse altogether. Well, assuming the PSU's connectors can take 2 x 2.5 mm2 copper :)

True, although that would be a case of something being "legal" but not sensible.

Can't think of any example of an appliance being wired in directly to a ring. All go via a plug or FCU. Very different from a radial.