On 14/08/2019 23:14, Ben wrote:
I started ripping plasterboard off to get a head start on the stud
walls, the
2 external walls were fine no issues, 1 external wall was fine, my first
issue
and questions are around the second internal wall which connects to our
neighbour, there are 2 boards deep, im assuming fireboard and plasterboard.

Is this property fairly modern and timber-framed ?. If so,
are each of the 2 boards grey in colour and 12.5 mm thick or is
one a pink colour ?.

Pink plasterboard is called fireline and is reinforced with fireglass.
It gives an hour of fire resistance (but it is the whole structure that
provides the protection not just the choice of materials).

If not pink, it might by green or blue, one of which colours is
soundblock plasterboard, if this is a party wall.

Whatever is there should not be changed, in fact, I'm not sure why
you are disturbing the deeper layer. Is is water damaged ?, or
are the two layers bonded with something that might be soundblock
goo or intumescent seal.