This has probably got a very obvious answer, but I'm blowed if I can find it.

How do you close a poll (prevent new votes being made), but leaving the topic open to replies?

You don't.

 

You don't.

 

Hmmm, think I better add my voice to that thread, surely being able to close a poll is a must?

Unfortunately it can't be done. If I had a top 5 list of requested features this would be in it. The topic you linked to from 2011 I suggested it in.