how to remove widgets from panel on plasma desktop?

[Gary Dale <garydale@torfree.net>]

Now that I'm finally back using KDE, an old problem has become front and 
centre again. Namely how to remove widgets from the bottom panel? I've 
got some that I don't want that just take up space but there doesn't 
seem to be any way to remove them.

And no, the widgets aren't locked.

Any ideas?