Cheers guys, I did my usual and asked a Q without having a look first.
Josephau, yup I know how to access the filter thanks. I had a good look when I was draining the breather tube, hence thinking about the sidepanel filter.

edit to add- the calsport vendor in peatbog's link here is cheaper on ebay than in their shop. Though in their shop they have remus pipes for the Ten...including a de-cat y-piece.

Additional edit to add...bought one