For the .co.uk you can file a dispute with Nominet if you think that the registration is an abusive registration.
An overview of the Nominet Dispute Resolution Service can be found here
[nominet.org.uk...]
Similarly for International TLDs a dispute has to be raised via WIPO (they certainly arbitrate the disputes anyway) see [wipo.int...]
[edited by: IanTurner at 11:12 am (utc) on July 21, 2008]