The DUP believes the building of a new MI5 headquarters outside Belfast, coupled with the "national security" provisions of the St Andrews agreement, marks a further entrenchment of the British state in Northern Ireland.
"This is a kick in the head for a united Ireland," suggested one senior DUP source last night, while confirming his belief that the proposed nomination of a DUP MP to Westminster's intelligence and security committee was "one of the most important things" to emerge from the St Andrews negotiations.
However, the SDLP poured scorn on the idea that membership of the committee would give the DUP access to privileged intelligence information or remove reliance on the Independent Monitoring Commission for continuing assessments of paramilitary activity in the North.
Yet senior party sources did not dispute DUP assertions that the detailed Annex E of the St Andrews agreement spelling out the future role of MI5 in the North would prove "deeply uncomfortable" for Sinn Féin.
The paper unveiled by Taoiseach Bertie Ahern and prime minister Tony Blair on Friday afternoon outlined the arrangements being put in place for the handling of national security intelligence and the necessary "accountability measures" that will be in place once "lead responsibility" passes to the British Security Service (MI5) late next year.
The change will bring Northern Ireland into line with the rest of the UK "to provide a consistent and co-ordinated response to the threat from terrorism, including from international terrorist groups such as al-Qaeda".
Despite SDLP insistence to the contrary, British officials say the change is a natural development from the Patten Commission reforms of the police in Northern Ireland.
Friday's paper also describes it as being in preparation for the eventual devolution of some policing and justice powers to the Northern Ireland Assembly.
While many PSNI officers reportedly fear an inevitable "mission creep" by the Security Service, Annex E says "new integrated working arrangements - the first such approach in the UK - will strengthen the PSNI's criminal intelligence capability".
This is because "PSNI officers will be co-located with Security Service personnel, and will work in a variety of roles, including as intelligence analysts/advisers and for the purpose of translating intelligence into executive action".
The paper goes on: "These arrangements are designed precisely for the purpose of ensuring that intelligence is shared and properly directed within the PSNI. Integration of personnel in this way is an essential protection against concerns that some intelligence would not be visible to the PSNI."
The paper stresses that "there will be no diminution in police accountability"; that the role of the Policing Board and the Police Ombudsman vis a vis the police will not change; and that police officers working with the Security Service in whatever capacity "will remain accountable to the chief constable and under the oversight of the Police Ombudsman".
Under the arrangements "the great majority of national security agents will be run by the PSNI, under the strategic direction of MI5".
MI5 "will continue to run directly a small number of agents who are authorised to obtain information in the interests of national security, as distinct from countering criminality."