As I understand it, OFCOM is not interested in licencing earth-mode kit as long as no "harmful interference to wireless telegraphy" is caused. To be honest, I think conduction modes are a total puzzle to them! Without (free) software ranges would be much shorter.
See https://sites.google.com/site/g3xbmqrp3/vlf/8-97khz-earth-mode-transmitter .