If you have double layer of plaster board the suggested fixing will not be suitable as they expand behind the board , they are likely to expand in the rear layer making a mess, the head is also very large making it unsuitable for many hanging fixture which require a specific size of screw. You could use a conventional plug if carefull as you have nearly an inch of plaster board, tighten screw slowly, or you could use these nylon fixings which allow a greater choice of screw.
http://www.screwfix.com/p/mungo-easi-drivers-nylon-32mm-pack-of-100/64161
They are screwed into the plasteboard using a screwdriver before fitting the screw, with two layers of plasterboard you will need a pilot hole or you risk tearing a hole.
http://www.screwfix.com/p/mungo-easi-drivers-nylon-32mm-pack-of-100/64161
They are screwed into the plasteboard using a screwdriver before fitting the screw, with two layers of plasterboard you will need a pilot hole or you risk tearing a hole.