Lord Carlisle found a ‘good level of attrition’ was achieved against a ‘very dangerous threat’

The majority of informers being used to combat this threat are being run by the PSNI.

There is also “solid scrutiny and review” of the interception of telephone and internet communications by the authorities to tackle violent dissident republicanism “in an environment in which communications technology is developing quickly.”

These are amongst the conclusions of Lord Carlisle, the independent reviewer of national security arrangements in Northern Ireland.

Lord Carlisle also found that the reliance on non-jury Diplock-style trials is reducing although “the residual serious and lethal threat of terrorism justifies the continuation of the non-jury system” here despite the desirability of jury trials as a norm.

Secretary of State for Northern Ireland Theresa Villiers outlined the main findings from the report prior to the dissolution of Parliament before Easter.

She said: “I have asked questions again this year about the relationship between MI5 and PSNI staff working alongside each other in security operations in Northern Ireland.

“Comments made to me in 2014 about the relationship between the two services were strongly mutually supportive. That they work together well and in the national interest is beyond question.

“The effectiveness of what they do is demonstrated by the successful disruptions that have taken place over the year.”

The use of informers - or Covert Human Intelligence Sources (CHIS) as they are known officially - has also been effective, she said.

“All activity and decision making concerning CHIS are documented carefully and European Convention on Human Rights issues are fully considered. There is a rigorous legal and policy framework for dealing with CHIS.

“The Regulation of Investigatory Powers Act (RIPA) 2000, and associated orders and codes, provide the legal framework for authorising and managing CHIS within the UK in a way that is compatible with the European Convention on Human Rights, and particularly the right to privacy.

“It requires that use of a CHIS is subject to prior senior officer authorisation, limits the purposes for which the CHIS may be used, ensures detailed records are maintained, establishes independent oversight and inspection, and provides an independent appeals mechanism to investigate complaints.”

Ms Villiers also addressed the continuing use of Diplock trials.

“I have also considered a number of issues relating to terrorism prosecutions including arrangements for the continuation of the temporary and renewable non-jury trial arrangements provided under the Justice and Security (Northern Ireland) Act 2007,” she said.

“The situation continues to improve. The number of cases requiring non-jury trial diminishes. The Director of Public Prosecutions for Northern Ireland uses considerable and proper care in the identification and selection of such cases. It is fully recognised that the norm is jury trial but the residual serious and lethal threat of terrorism justifies the continuation of the non-jury system.

“There is no evidence of any disadvantage in terms of outcome to defendants in the current system of non-jury trials. They are as likely to be acquitted as in jury trials, and have the advantage of reasoned judgments, and less inhibited access to appeals. Part of the criminal justice setting in need of appraisal is sentencing in terrorism related cases. Generally such sentences are considerably shorter than comparable sentences in England and Wales, with notably different tariffs in murder cases,” she said.