Thanks for your response. I realised that we're using a reset.css stylesheet that basically wipes out all default styles.
To overcome this I had to create a style in my stylesheet then add a class attribute to the RadHtmlPlaceholder (as per this post
) and that seems to have fixed it.
The only issue I came across was that the RadHtmlPlaceholder seems to wrap the content in 2 divs, so to keep IE happy I have to apply the class to the inner div because if I add to the outer div, the <ul> doesn't pick up the style definition (although this works fine in FF)