In article , Mike Dodd
wrote:

Now, I think I'm right in saying that plasterboard fixings are not
appropriate here - I need the fixing to go into the blocks behing the
plasterboard. BUT, the block fixings that I've seen are intended for
direct mounting (i.e. the head of the fixing is flush with the block -
I've got the small issue of 12mm of plasterboard + air gap in the way.

80mm hammer in wallplugs like Screwfix 13953 or frame fixings (17286) or
other lengths to suit did the trick fine for me when I put a shelf on a
dry lined wall recently. Don't hammer them hard though or you could push
the plasterboard back towards the wall, just tap them in gently until
they line up with the surface and tighten up the screws with a
screwdriver.

--
Mike Clarke