Filing isn't as straightforward as it may seem, as the striker plate
doesn't simply have a rectangular hole in it for the latch to pass
through, it has a box around the hole: (eg like
http://www.thediyworld.co.uk/images/locks/lock-striker.gif

Might try and see if I can find a different striker plate in fact,
without the box, and which may well also have screw holes in a different
position...

Filing a boxed one is tedious but still doable. That is one reason to
use engineering blue/dry marker pen to find the high spots that jam
since you want to do as little work as possible!


If it's only 1-2mm, you could alter the screw holes in the striker
plate, so they are oval. That's probably the easiest bodge of all with
one of those rotary files in a drill - takes a few seconds and job done.