Trev's tip sounds like a good'un.
"sounds a lot of work if a file does the same job though"
Using Trev's method there's every chance a lot of the distorted thread can be persuaded to reform. A file is only going to remove metal.
I've had success in the past using a small chisel and very small (!) hammer, to gently push deformed metal back into place, rather than file it away. Not so good for major distortion though.
