Thanks for the replies folks - most helpful. There seem to be a couple of main solutions here - the frame -fixing type that get their true fixing in the wall behind the board, - and the hollow wall fixings that expand directly behind the plasterboard. They all have their strengths and weaknesses.
I am going to have to use a mix of types to sort out all the bits and pieces I need to fix to the wall. Apart from the shelves - for which I will be using the frame -fix type - there are pictures and curtain-poles. Curtain-poles need a firm fix, but the hardware isn't necessarily designed to take large diameter screws , found in frame fixings
.
I guess it's going to be a case of 'trial and error' to find the best solution.