Mould inside double glazing gaskets

[Whoever]

I am experiencing black mould building up between the external double glazing gaskets and the outside glass window pane, i.e. it's visible from inside the room. As the gaskets are white it's very unsightly. What's the best way of getting rid of it please?

[The Builder]

Make sure I've got this right............ you don't mean the spacer between the panes which is usually silver or brown? You mean the white uPVC bead on the outside, that keeps the glazing unit in place?