Thanks.I have tried both the "line and paragraph spacing" and the "no spacing" solutions and both work while I have Word 2010 open but neither are saved so when I fire it up again the double spacing returns. Is this simply a default setting which can't be changed permanently?
Open normal.dotm. Go to the Styles pane > Manage styles button > Defaults tab. Make your changes there. Save and close normal.dotm. If you want to use table styles or themes and style sets, leave the normal paragraph style unmodified.