I'm surprised it's got an earth in there - but hey, it's there, use it. ...
It should be one or the other, you either have the piece with the ball in or the filter
Is it practical to improvise a paper dust bag? I use them on my VAX and even with oily swarf they last till they are about full and it makes getting shut of the waste much more pleasant - I buy copies of the original fit ones for about ten pence each from Amazon.
It would still need the cage to hold the middle of the large filter from being sucked up I think, the filter round the cage is only like pantyhose thick, I don't really see any harm leaving it there.
I have a Henry,Edward and a George. When you are doing wet stuff you run the cage with the ball. When doing dry stuff you run the white filter piece which should have a round plastic frame in the bottom of it. If you have the cage with the ball then then there is no way a bag would fit/work. I am surprised the filter piece will even fit with the cage in as they both fit between the lid and the tub.
A Charles should be the same., there is another model which uses a slightly different system so maybe you have that.