MI6 failed to make clear to the Foreign Secretary that one of its spies overseas had gone rogue and engaged in serious criminal activity, a new report by Britain’s intelligence watchdog has revealed.

The intelligence agency had been asking for renewed authorisation of the agent’s activities without being clear about the agent’s behaviour, the Investigatory Powers Commissioner’s Office (IPCO) latest annual report says.

IPCO has censured MI6, or the Secret Intelligence Service (SIS), for a range of shortcomings in its handling of its agents in the report, saying the Government “ought carefully to consider” if tighter oversight is needed over the operation of Britain’s spies abroad.

We concluded ... SIS’s ‘red lines’ had most likely been breached, but the renewal submission failed to make this clear

The watchdog said the case of the rogue spy had come to light in a review of a submission made by MI6 under Section 7 of the Intelligence Services Act, used to allow British personnel to commit criminal acts in other countries.

IPCO reviewed the case of what it called the “high-risk” agent, who SIS had discovered “may be involved in serious criminality overseas”.

“SIS did not encourage, condone or approve any such criminality on the part of their agent,” the report says.

SIS had gained the agent’s “full transparency about the activities in which the agent was involved”. The agency had then spelled out some clear “red lines” governing “conduct that was not authorised and would result in the termination of SIS’s relationship with the agent”.

“On renewal, six months after the original submission, SIS set out a number of indicators that the agent may have been involved in, or have contemplated, the serious criminality referenced above,” the IPCO report says.

“We concluded that, on the basis of this new information, SIS’s ‘red lines’ had most likely been breached, but the renewal submission failed to make this clear.”

IPCO said while SIS’s submission provided information about criminality that may have occurred and noted an increased risk in the case, “it did not make expressly clear (to the Foreign Secretary) that SIS’s ‘red lines’ had probably been crossed”.

“We concluded that the renewal did not provide a comprehensive overview of available information which we believe would have provided the Secretary of State with a fuller and more balanced picture,” the report said.

While the report says SIS had “immediately responded to these concerns” by updating the Foreign Office, Human rights group Reprieve said revelations showed MI6 needed to greatly improve how it handled its spy network.

“While our intelligence agencies do a vital job, this report rings alarm bells in its account of agents run amok,” Reprieve’s deputy director Dan Dolan told The Guardian.

Mr Dolan said the Government “urgently needs to get a grip on unchecked lawbreaking by agents”, but that ministers were “rushing through legislation which places no clear limits on the crimes they can commit”.

Commenting on the report on Tuesday, Prime Minister Boris Johnson told The Daily Telegraph: “This Report demonstrates the high quality of the oversight of our security and intelligence agencies’ use of the most intrusive powers. I am satisfied that our arrangements are amongst the strongest and most effective in the world.”