Britain’s internal secret service MI5 has been criticized for breaching laws on a serious level when it comes to storage and handling of the data gathered from citizens with the purpose of fighting terrorism.

The Investigatory Powers Commissioner said during a hearing in UK’s High Court on Tuesday that the MI5 had repeatedly used “special measures” to obtain data under warrants but it had failed to comply with the laws on how it should retain and delete data.

The watchdog said the violations committed by the MI5 in handling large amounts of data  were “of such a gravity” that judges should think twice in future before granting warrants meant to enable the security service to gather information.

The case against the MI5 has been brought by Liberty, a civil rights advocacy group, which has argued in the past that the intelligence service has benefitted from many “probably unlawful” warrants to carry out its work.

UK admits MI5 breached surveillance safeguards

UK interior minister admits the MI5 has acted in “serious” breach of surveillance safeguards.

It believes the MI5 has breached the Investigatory Powers Act repeatedly when dealing with targeted interceptions, hacking of phones and mobile devices and bulk data gathering, including information created by the citizens when they use the internet or other forms of communication.

The MI5 has reportedly used the massive powers as parts of its counter-terrorism operations.

Adrian Fulford, the judge overseeing the case in the High Court, said on Tuesday that he had found a “historical lack of compliance” with the law in the way the MI5 had handled data.

Fulford said there was a need for the MI5 to prove in the future that its systems are fit for purpose “to a greater degree than usual” if it wants to apply for warrants.