Scrollview with Stacklayout - no scrolling

Hello,

I am attempting to place a stacklayout into a scrollview. Unfortunately, the scrollview doesn't seem to be able to scroll. This is the case both in the iOS simulator and on the iOS device (iPhone 5S). Is there something I am doing wrong? My code is below. Note that I am using my Markdown parser to convert content from markdown into Labels, Images and (not strictly markdown) Buttons, but this shouldn't affect how the scrollview/stacklayout work together.

        private ContentPage BuildContentPage()
        {
            var contentPage = new ContentPage();

            var stackLayout = new StackLayout()
            {
            };

            foreach (var line in _pageLines)
            {
                stackLayout.Children.Add(line.DrawLine());
            }

            ScrollView scrollView = new ScrollView () 
            {
                Content = stackLayout
            };
            contentPage.Content = scrollView;
            return contentPage;
        }

The method call line.DrawLine(); returns a View that is converted from Markdown. For example, BodyPageLine has a DrawLine method that returns a Label with the content of the line:

public class BodyPageLine : IPageLine
    {
        public string LineContents { get; set; }

        public View DrawLine()
        {
            var label = new Label();
            label.Font = Font.SystemFontOfSize(NamedSize.Medium);
            label.Text = LineContents;
            return label;  
        }
    }

Hopefully, this is an issue that can be solved easily!

Thanks,
Richard