But the demonstrators who have taken over parliament and massed in the surrounding streets for the past five days fear the deal could further swell Beijing's economic influence over their proudly democratic island. (Source)
I'm confused about what "further swell" means.
My perception: ... they fear that the deal may more and more (further) make the Beijing's economic influence bigger or swell it in their democratic island.
My second concern is why the writer says "their proudly democratic island." What is the relation between democratic island and proudly and swell?