What is the easiest way to remove old emulsion paint from a plastered wall?

When I removed the old wallpaper, some of the old emulsion paint underneath
came away with the paper in many places, and the differing levels would
show up if I simple painted over everything. So Ideally I'd like to remove
all the old paint, if it's not too much of a PITA to do.

Failing that, can anyone suggest a way to sort of fill in the bits where
the old emulsion came away? Polyfilla perhaps?

I don'tt want to re-paper the wall; I want to use emulsion for the final
finish.

Many thanks

Al