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What type of shelving is it? If the brackets can work with it, as above I would try to get the plug in to the brick behind the plasterboard and use that to take the weight rather than the plasterboard itself. If that's a no go, hollow wall anchors are good (as above, again), but they are long, so you will need to drill out some of the masonry behind the plasterboard.
Dot and dab is a shit show really isn't it?
Installing string shelving onto plasterboard walls, attachhed is photo of the screws and plugs they supply
2a. do i need shorter screws with matching head shapes to the provided ones?
2b. do i need to drill the brick behind and use the provided ones?