Gavin - there's been some discussion of the copyright problem in a few other youtube threads.

You can object to their assertion. IIRC they flag the video and there's a button/link where you can state your case that the copyright doesn't belong to someone else. I had this on one of my videos (a Carolan tune I think). All I said was that the composer had been dead since whatever date and that the arrangement was mine. The flagging disappeared and nothing else happened. Just state that it's a traditional song and your arrangement and you should be fine.

Mick