In reply to Tree:
> Your pictures look like a decomposing fungus: I'm probably wrong though...
Maybe. The goo was pretty much colourless and very translucent, not like a mushroom, but possibly some sort of slime mould. It was very much engulfing the plant stems around it, though not obviously affecting them. The yellow bits were quite discrete, and looked a lot like those I've seen on 'blooming' lichens.
It might be something different from the ragged jelly chinks I've also seen before (similar to the one Mike Peacock linked to) - I don't have a good reason for thinking it's the same thing, really.