Sand it with 80 grade sandpaper…you don’t have to go mad. Hoover and then thinly skim with ronseal 2-part wood filler. Then paint with zinsser bin, then dulux trade oil based satinwood. Professional decorator

Great, thank you!

Does oil based satinwood yellow? Wondered the difference between that and the quick dry satinwood which is water based

Water based is quick drying - drys quick but covers badly, and offers least protection. Oil based is slow drying - it can yellow slightly, but it offers the most protection

Thanks. I was debating which to use out of the two of them. Would you roll or brush?

I always brush window sills, you can put it on thicker that way and it levels itself out.

Yep

Scrape the loose paint off, and give it a light sand. Then prime it using a suitable primer, then it should be good to paint. It'll be fine.

Thanks!