Tramp not engaging

I use tramp a fair amount and generally just works awesome. Recently it has
stopped working - simply not engaging when I would expect it to, i.e. C-x
C-f /ssh:uname@host:~/ at which point I would hope to start seeing some
autocompletion. However I see nothing and if I fille the path myself and
open it appears that the file is looking to be resolved locally as a new
file.

Not sure where to start debugging, any pointer would be greatly appreciated.

Thanks,
 -Harvey