THE government is refusing to confirm whether MI5 agents have a “licence to kill”, the Investigatory Powers Tribunal heard today.

Lord Justice Singh said that the case, brought by an array of human rights groups, may involve “fundamental” constitutional issues.

Campaigners are demanding to know if undercover agents are allowed to commit murder and torture.

Spymasters claim that revealing the rules their agents work under would allow terror groups to detect informers.

At the tribunal showdown, it emerged that MI5 operates what it calls a “parallel” policy to the Regulation of Investigatory Powers Act (RIPA).

Parliament passed RIPA in 2000 to govern how police and intelligence agencies use covert sources — and it prohibits agents from committing crimes.

The court case, which began nearly two years ago, has already seen some sections of MI5’s secret “parallel” policy disclosed, revealing: “It may sometimes be necessary and proportionate for agents to participate in criminality in order to secure or maintain access to intelligence that can be used to save life … or to ensure the agent’s continued safety, security and ability to pass such intelligence.”

The government is refusing to say if this parallel policy means agents can commit murder or torture in order to maintain their cover within a terror cell.

The case is brought by Privacy International, Reprieve, the Committee on the Administration of Justice and the Pat Finucane Centre.

Pat Finucane was a Belfast solicitor who was assassinated by loyalist gunmen in 1989.

It later emerged that the killers’ intelligence for the attack came from a British Army agent.

On Wednesday, in a separate case, Britain’s Supreme Court issued a landmark judgement that said the government has never properly investigated Mr Finucane’s death.

The Supreme Court found that a review commissioned by David Cameron, which was published in 2012, was inadequate.

Just weeks before Mr Cameron published that flawed report into Mr Finucane’s murder, the then prime minister hastily wrote a secret letter to Britain’s intelligence watchdog admitting there was a “long-standing” covert policy to let MI5 agents break the law stretching back to the early 1990s.

It was only in 2012 that Mr Cameron asked the intelligence watchdog to belatedly begin monitoring that policy — the full content of which is still being kept under wraps.

The tribunal challenge continues.