AJB wrote:

Tweaking some lighting, I turned off the mcb for the LX circuit and
opened a pendant fitting. Double-checked with a neon 'driver - not live,
is says. Unscrewed one of the neutrals. As I do so it sparks quite
impressively. Why?

A couple of possibilities...

As others have said there may be a crossed circuit of some description.

A spark must means there's current flowing - but where from? I did
wonder whether the 12v transformers for the halogens might have caused
it?

You did not say where you got the spark from (i.e. if it was to the
neutral connector itself, or to earth). If it was to earth you need to
remember that a neutral ought to be regarded as a live conductor. It may
have a voltage on it that is some way away from earth potential. How far
will depend on how "stiff" the supply to your property is and how many
other properties share "your" neutral. The result is that it can be a
few volts above ground - certainly enough to pass a reasonble current to
earth.

--
Cheers,

John.

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