I have taken my four and a half inch skirting boards off during renovation as they protruded from the wall to the inside of the boards by at least a quarter of an inch. On investigation the boards bow from bottom to top. Also the plastering falls short of the floorboards by two inches or so.
My feeling is I need to skim the bottom of the boards (can't buy any at the moment anyway) with an electric planer and replaster the wall. Anyone disagree?