Its always null? When Html.RenderUserControl is called is the ViewContext not passed on?

Unfortunately, you're correct. Only the HtmlHelper and UrlHelper objects are initialised.

You can get at the context by doing Html.ViewContext

---

Here's the snippet from reflector

private static string DoRendering(ViewUserControl instance, ViewContext context, object controlData, object propertySettings)
{
  ViewPage sourcePage = new ViewPage();
  sourcePage.Controls.Add(instance);
  sourcePage.Url = new UrlHelper(context);
  sourcePage.Html = new HtmlHelper(context);
  SetUserControlProperties(instance, propertySettings);
  if (controlData == null)
  {
    instance.SetViewData(context.ViewData);
  }
  else
  {
    instance.SetViewData(controlData);
  }
  return HtmlExtensionUtility.RenderPage(sourcePage);
}

 
 What *should* happen is sourcePage.ViewContext = context and they should do lazy initialization of the HtmlHelper, AjaxHelper, and UrlHelper objects.