Having scoured the internet, I came up with a couple of ideas, and believe this one is quicker for straight and curved rail, and the fishplate remains in tact, photos to explain:
First the track length with the fishplate and a short length of spare rail:
Inset to spare rail in the fishplate to be removed until it but upto the rail with the offending fishplate, then grip the fishplate in a bench vice, tight enough to hold, but not squeezed.
A sharp blow with a hammer on the end of the spare rail, and both rails will slide in the fishplate.
A second (or more depending on how hard you hit the rail, and the fishplate is all but off the track.
Track, rail and fishplate, with minimal damage to the track or fish plate.
This is a variation on a method I saw on the internet and was dubious if it would work, but it does, only removed 10 fishplates so far, but works every time. However for points (switches) Greg's method is the only one that will work.