British intelligence agencies have policies allowing staff to access confidential communications between lawyers and their clients, official documents have revealed.
The guidance was disclosed for the first time at a tribunal which examines complaints against MI5, MI6 and GCHQ.
The lawyer-client relationship is generally protected by strict rules.
Campaigners said the disclosure had “troubling implications for the whole British justice system”.
The government could be handed an unfair advantage in court if it had access to confidential materials, they said.
In one case, MI5 revealed, legally privileged information had been inappropriately passed to lawyers defending the security agencies, where “the potential for tainting” was identified.
The Investigatory Powers Tribunal (IPT) heard that updated MI5 guidance published in January advised lawyers that while there was no “legal prohibition” on reading privileged material relating to their cases, doing so should be “avoided” to prevent prejudicing proceedings.