my dad however says that plasterboarding and skimming causes damp
where as normal plastering wouldn't. The wall in question is an
outside wall in a mid-terrace bedroom.

Neither method will solve a damp problem. Penetrating damp can be solved by
pointing the outside of the wall, and ensuring that there is no soil piled
up against the wall. Rising damp doesn't exist. Condensation damp would be
solved by insulating the wall, such as by using Kingspan K17 board to
dryline instead of standard plasterboard.

Christian.