Sinn Féin has welcomed today's proposals by the British government to separate the PSNI and MI5.
The party's spokesman on justice and policing, Gerry Kelly, said that the proposal's would go a long way towards achieving "a new beginning on policing".
Mr Kelly said: "Our [Sinn Féin] objective has been to firewall local policing from the malign and corruptive control of MI5".
"For decades people across this island have suffered enormously as a result of the activities of MI5, which has been responsible for collusion and state sponsored killings in Dublin and Monaghan and across the north.
"The proposals today remove MI5 from policing structures in Ireland".
Under the new proposals MI5 and the PSNI are to be completely distinct and separate bodies with no police officers seconded to or under the control of MI5.
Interaction between the two organisations on issues such as international terrorism would be by way of liaison, with a small number of police officers based at PSNI headquarters in contact with the security service.
SDLP leader Mark Durkan said Mr Blair's statement would limit the ability of the Police Ombudsman to investigate national security issues. He also argued that MI5's role would not be restricted to national security.
"MI5 will still be taking over work on national security and it's not just on international terror but home-grown paramilitaries too," be said. "A careful reading of the statement today — along with other indications — confirms this. And let's be clear, this supposed 'separation formula' will damage accountability.
"The fact is that the Police Ombudsman can investigate national security matters now. When MI5 takes over, she will not be able to - and will have no power to make them give her information.
"So when anybody has cause for concern or complaint about national security intelligence-gathering, unlike now there will be nobody credible to turn to."
Mr Durkan accused Sinn Féin of seeking a "short-term fig leaf" in the British prime minister's statement but warned that in the long term the British government would be in control.
"None of this is to say that Sinn Féin should not sign up to policing.They owe it to victims of crime to work with the police. "But they also owe it to the public to be honest about MI5 and should be working with us to get these problems resolved."