Resx + UWP app

Hi I'm trying to add a UWP app to my Xamarin.Forms project.

I'm using a .resx in a Portable project that contains all the strings used in my application. This works fine for Xamarin.iOS and Xamarin.Android but I'm having problems with the UWP project. Although it compiles successfully all the strings in the code return NULL rather than the text in the appropriate language.

I'm using a shared project for my shared UI XF code. I'm accessing the resource file through the methods that it generated e.g.

{namespace}.{ResourceFile}.{Key}

Has anyone had the same problem and resolved it?