Just something worth pointing out for Plusnet account holders. They dont specifically block ports to curtail the use of p2p.
They do use Ellacoyas which would not be fooled by a simple port change as per the experience above.

Therefore something worth checking is that you dont have the "Safe Surf" option set in your account preferences.
This is intended as a parental type control which can be configured by the main account holder at https://portal.plus.net/surf/

Port 6346 is one of the many ports that can be blocked using this setting.