Never seen anything remotely like asbestos boxes (thats not to say they didn't exist). That looks a lot like an old wooden box, but hard to tell from the picture.
worth showing your findings to whoever ordered the work, there are companies to call for inspection and removal of the stuff.
if they not bother then invest in a proper mask and a tyvek suit if you planning to disturb it.
Have only seen wooden back boxes that look like that, think it's just old and not been loved, take it out and send some more pics, might be wrong as l am only 48 maybe some one like tel can shed some light on it
It looks like it could be what we used to call 'millboard' when I was an apprentice. Usually it was used in wooden cupboards that had electrical equipment in them. We used to get it in a large sheet and hand-cut it into panels to internally clad the cupboard to make it flash-proof or fire resistant. That said I've never seen it used on its own in cement but I'd suggest you get it checked out according to whatever your local regulations dictate. Without seeing the texture of it first hand and giving it a prod with a screwdriver it's impossible to say if it's asbestos or not.
Agree it looks like a regular wooden back-box. The sides usually taper to a thin section around the front edge that we can see, which makes them look thinner than they are and more like a sheet material. If you touch a drop of water on the cleanest part you can find, the colour of the wood might show through, and you won't disturb any dust. I have also never seen a light switch box made of asbestos cement board.
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