Can I Replace Plasterboard with Tile backer board (Build regs compliance)?

[richb78uk]

We have a dormer constructed, passed by building control, but they have obviously just plasterboarded everywhere, can I remove this from the ensuite walls (external ie dorma walls which are timber stud construction filled and covered with kingspan) and replace with foam tile backer boards of equal or greater thickness?

 

[Bond]

Can’t see any problems in doing that, or easier if circumstances allow, retain the plasterboard and overboard with tile backer board.