I finally managed to get hold of some rivets - I first tried getting some online but they sent me the wrong ones twice so I gave up and went to the nearest BMW parts centre.

Seeing how they worked, I quickly deduced how to get the old ones out, that took only a minute. Popped the old moulding off and put the new one on. Put the rivets in but now am completely unable to fit the rivets. Using plyers hasn't worked because of having to hold them down at the same time as pulling - I've managed to get three to pop just outside of the trim rather than inside. I'm guessing I need a tool for this but everything I've seen is for metal rivets and costs ~£25.

Any tips on how to pop these rivets without spending loads on a one use tool?