Thanks for the feedback. Put cuts of 35x60 mm timber between the vertical plasterboard battens. Can I screw the brackets just into these (35 mm thick) or should I go through the wood and into the block behind?
My builder tried to prepare the kitchen walls for the wall units but ended up fixing batterns behind the plasterboard too high, about 30/50mm. I am now thinking If I can get away with installing the units using the supplied brackets just into the plasterboard (decent drywall fixings), use them...