Render web user control in a web service

[WebMethod(EnableSession = true)]
[ScriptMethod]
public string RenderControl()
{
            StringWriter tw = new StringWriter();
            HtmlTextWriter hw = new HtmlTextWriter(tw);
            string searchResultHtml = "";
            Page page = new Page();
            ScriptManager sm = new ScriptManager();
            HtmlForm form = new HtmlForm();
            HtmlGenericControl div = new HtmlGenericControl("UserControlDiv_DisplayResults");
            ucDemoControl userControl = (ucDemoControl)page.LoadControl("~/Controls/ucDemoControl.ascx");

            //init controlm properties like datasource or other

            userControl.DataSource = null; //add something here

            page.Controls.Add(form);
            form.Controls.Add(sm);
            form.Controls.Add(div);
            div.Controls.Add(userControl);
            HttpContext.Current.Server.Execute(page, tw, false);
       
            searchResultHtml = tw.ToString().Substring(tw.ToString().IndexOf("<UserControlDiv_DisplayResults>") + 30);
            searchResultHtml = searchResultHtml.Substring(1, searchResultHtml.IndexOf("</UserControlDiv_DisplayResults>") - 1);
        return searchResultHtml;
}