Was it silk paint you got on your skrtiings?
As that is harder to get off, but saying that, any emulsion paint with a bit of elbow grease should come off.
if all fails, then invest in a bottle of brush cleaner, you will find it alongside the whitespirit in any DIY sheds.
Its a blue liquid and mainly its for to clean brushes, but its marvelous stuff, and will remove any paint from anywhere.
All you do is brush it along the offending area, perhaps a couple of times, then get one of those scourer thingys, not a new one, but an old one, or a good cloth, and it will come easy peasy.
Take note...... you should paint your skirtings last, (unless its finish paper), but if you do paint your skirtings before you have finished emulsioning the walls, the trick is to wipe the skiting with a wet cloth, and when you finish the wall, go over the skirting again, with a damp cloth, this will stop the paint settling on your skirtings.