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@benbrangwyn
If the rub happens only at certain points in the rotation, that would indicate that your chainrings aren't true. (And there's likely to be other problems as well). It's easy to check trueness by watching the chainrings relative to a static point as you turn the cranks. Depending on how bent they are (and whether they're bent nearer or further from the axle) you can use an adjustable spanner to straighten them out. I've used a mallet before and it's worked reasonably well for a lousy steel chainset. But if it's something a bit better (and your's is), then the adjustable spanner is one answer.
Once your chainrings are true, then you can look into the other issues.