Bulk data collection 'helped MI5 prevent dissident republican attacks'
MI5 powers to gather large amounts of data helped foil dissident republican attacks and put suspected perpetrators in court, a major review has said.
Telephones belonging to members of anti-peace process armed groups were identified, leading to the recovery of explosives and the arrest of an individual committing a terrorist offence before any harm was caused.
Bulk powers are among the most controversial tactics set to be covered by new UK surveillance laws.
They are used to access communications data - the who, when and where of an email or text message but not the content - in large amounts.
Terror laws watchdog David Anderson QC wrote: "Bulk capabilities are essential to understanding the plans of resilient, experienced terrorists and stopping their attacks."
The secret services acquired the information in large volumes and used it to generate intelligence about threats that cannot be obtained by more targeted means.
Some privacy campaigners have raised concerns.
The techniques were seen in a recent operation to identify phones linked to a dissident attack in Northern Ireland, Mr Anderson's report said.
The information helped lead to the arrest and charge of an individual with terror offences.
Telephones not previously known to MI5 were identified.
The report said: "It would have taken more time and been considerably more resource-intensive to discover the telephones without bulk acquisition data."
The method was used in 2014 to identify a mobile phone being used by a dissident.
It was intercepted and police were able to arrest the individual while he was committing an offence, and he was prosecuted.
It would have been possible to identify it without bulk data, the report said.
It added: "However the alternative method would have involved significant collateral intrusion in the form of gathering information about many telephones, all but one of them of no intelligence interest.
"This method would also have taken longer and so carried the risk that the correct phone might not have been identified in time to prevent an attack."
In 2013 it was suspected that dissidents had already obtained explosives and their activities were increasing in a common sign of an imminent attack.
However, MI5 did not know the date of any proposed attack and the group's security awareness made it difficult to obtain further information.
The bulk data identified telephones being used by the group and enabled MI5 to trace previously unknown group members.
The review said: "MI5 was able to increase its coverage of this expanded group.
"As a result, it became aware of a sudden further increase in activity from analysis of the group's communications activity and MI5 judged that an attack was imminent."
Police intervened and recovered an improvised explosive device. A prosecution followed.
Mr Anderson said dissident republicans continued to conduct operations designed to kill members of the security forces including police and prison officers.
Last year there were 16 attacks and this year prison warder Adrian Ismay died following a bombing.