I checked the proxy settings in Preferences and it looks like a timing error on my part. I completed the Host, Port, Username and Password fields some time ago. However our organisation (and I'm sure many others) ask you to change your password on a regular (e.g. monthly) basis.
I had set a new password recently on my work network but didn't update the SoapUI Proxy settings accordingly. Password has subsequently been updated on the proxy settings and I can see the project now in my SoapUI session.