Finally got this sorted, albeit not the ideal solution
Go to the web management screen
Network > IP Address / properties
Set the Automatic via DHCP option to "enabled"
The DNS settings awere set as per my local network (gateway and DNS), but as soon as i set to DCHP enabled, the torrents started working again.
I don't know how to notify a support mod, but it would be nice for a "test settings" button on this screen to confirm the manual settings are correct.
I don't like having a floating ip address for the linkstation but as it is on most of the time, it may be ok, just need to use the nas navigator to find it