Bathroom: plaster walls and ceiling - Plastering job in Malvern, Worcestershire

Job description

I am replacing old suite and tiles with new ones.
The new bath is being moved from under a window, along the same internal stud/plasterboard wall (currently tiled) to the other end of the room against another internal stud/plasterboard wall (currently only painted).
The bath will be used as a shower in the plasterboard corner.
I am carefully removing the existing tiles from the plasterboard walls which is leaving a pretty good surface (plasterboard is not broken but some of the cardboard surface has been removed by damp and there are patches of old adhesive). The plaster itself does not seem to be affected by damp but I have not yet removed the tiles behind the current shower.
Main wall (tiles being removed): 2.4x2.2m
Other wall (painted): 0.75x2.2m
Ceiling (currently artexed): 2.4x1.6m

I have read around and aquaboard is recommended for a shower area but since the plasterboard is ok I was hoping to get away with a plaster skim to seal the partially damaged existing board and maybe just tile straight over the painted wall?
Any advice also gratefully received.

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Feedback for Cyriack Hooper Building and Plastering

Cyriack's plastering work is excellent but the new plasterboard was put up to leave a bowed wall of about 2 inches which I wasn't expecting. The tiling should hide it, but I was hoping for a perfectly flat wall considering it was brand new plasterboard.
In future consider putting stud work to prevent the same problem.

Cyriack Hooper Building and Plastering's reply:

Plasterboard was new however the studwall (four battens wedged sideways from floor to ceiling?) were bowed - plasterboard took the shape of what it was fixed to. Should have fitted a new studwall as I first suggested.