Clicking View Details, doesn't show anything useful.
Apparently nothing had changed on the environment, so it wasn't obvious what had happened.
I thought a good place to start would be to open Lync Management Shell and upon doing so was create with this:
So it appears for some mysterious reason the Execution Policy on scripts has changed
A quick change to RemoteSigned by running Set-ExecutionPolicy RemoteSigned fixed both the crash on downloading the topology and the error in Powershell.
Still can't explain why this happened!