Part of having a fair trial includes having legal representation, and the ability to communicate with your legal council in confidence.
Eavesdropping on privileged lawyer-client conversations, regardless of legality is outrageously indecent and should be illegal. Revoking a lawyer's visa because he is representing a particular client is equally outrageous, especially due to the chilling effects it causes upon the legal community making it much more difficult for suspects of serious crimes to find good legal representation.