Just thought I would create a post to recommend a new type of plasterboard fixing on the market that I have been using. Grip It Fixings.
Its a universal fixing that caters for Dot and Dab, Cavity Walls, Insulation back plasterboard and double thickness. I have been using them for attaching radiators and the like to walls where my brother who is a kitchen fitter is using them to hang cabinets.
Would strongly recommend that you have a look at them and give them a go because to me its a solution to a long lasting problem