Can't really say I can spot the worn sprockets with my eye but I changed my chain about the same time (after 3000km from new) and went through the whole skipping thing. Chances are good it is the rear sprockets that need replacing - mine did - good thing they are cheap and easy to change.
I don't like the stock Brompton chain - when I measured a new one, it had already stretched from ideal. My theory is that since they come "pre-stretched", they wear the sprockets down faster than a chain of the correct length.