[Arran]

Ron;
  There is a trick that I learned of a number of years ago for fixing runs, drips, or sags, without having to sand it down, it's a razor blade. Apparently auto painters use this trick all the time, they shave or scrape it down with the edge of a razor, the reason being is that the run is always thicker then the surrounding paint (or lacquer) and it's usually not fully cured all the way through so they tend to clog sandpaper. After you shave the high spots off, and leave it to cure for a day or so, then you can wet sand it to blend in with the rest of the paint. I've been using this trick for years and it works quite well.
Regards
Arran