I think Planet X hubs are manufactured by Novatec they do several different models so a search of the Novatec catalogue will be required to determine which is yours.
a bit of advice here,
http://www.bikeradar.com/forums/viewtopic.php?t=12942960&p=18552259
a bit of advice here,
http://www.bikeradar.com/forums/viewtopic.php?t=12942960&p=18552259