I am putting in a new (eBay) fireplace wooden surround and will need a
panel of some sort to cover the mess that was originally there
(wallpaper with bits missing, and a hole for a gas fire flue). Can I use
normal plasterboard or does it (should it) be the fire panel stuff like
this:
https://www.wickes.co.uk/Knauf-Fire-...-2-4m/p/190539
Or something else?

I don't want the expense of a marble (or other composite pretend marble)
back.

Ta.