Thanks for your response Suresh.
This looks like it will achieve what I'm looking for. However I'm not using SfChart here but Chart. I tried using this code but it didn't work:
Axis.StripLines.Add(new ChartStripLine() { Stroke = new Pen(Brushes.Black, 2), IsEnabled = true, Start = StripLineStart, Width = StripLineWidth, Interior = Brushes.LightGray });
I took a look at the sample you attached and noticed that the gridLines and minorGridLines under the Strip line are not visible. Can something be done about that? If not then I'll just settle for using the Annotation but I don't think that is supported in the Chart object (only the SfChart). Please correct me if I'm wrong there.
Thanks again.
James