looks like caterpillar damage, I believe it is from a moth? Having had similar damage to some of my plants. Did you notice any leaf curl earlier on? If you can see any just peel open the leaf and you will probably find a bit of spun silk holding the leaf closed, and most probably a small caterpillar up to about 1/2 inch in length, if so just remove. The plant will recover,as it did for me.

Thanks Kev...nothing to do with the big red fly on it then?

looks like chewing damage and the fly isn't linked to it really.
just cut off the affected parts and bin. the plant will recover.

Thanks, I will.