I was able to add individual category page Title, Description and Keyword tags to each category page using the following code. The category name becomes the page title, short descrition the page description and the long description (I have amended the CMS to use this for keywords) gives the keywords.
this.Title = category.CategoryName;
HtmlMeta hm1 = new HtmlMeta();
HtmlHead head = (HtmlHead)Page.Header;
hm1.Name = "Description";
hm1.Content = category.ShortDescription;
head.Controls.Add(hm1);
HtmlMeta hm2 = new HtmlMeta();
hm2.Name = "Keywords";
hm2.Content = category.LongDescription;
head.Controls.Add(hm2);