Guidance was drawn up for Stormont officials on how to operate in the absence of unionist ministers.

It came following the resignation of then-first minister David Trimble in July 2001, followed by his Ulster Unionist ministers and DUP ministers in October after no movement on the decommissioning of terrorist groups.

SDLP and Sinn Fein ministers remained in post.

The Northern Ireland Assembly first met in July 1998 following the historic Belfast/Good Friday Agreement in April.

But the row over decommissioning – with unionists refusing to work with Sinn Fein until the Provisional IRA had handed in their arms – caused a number of periods of suspension.

Guidance issued for departments following the resignation of ministers in October 2001 has been revealed in previously secret official files.

It said the Executive cannot operate under the “sole authority of the ‘Acting’ Deputy First Minister”, and therefore the Executive cannot meet, memoranda for consideration by the Executive cannot be agreed and memoranda cannot be circulate for agreement by written procedure.

For the departments operating without ministers, the note said no correspondence can issue under ministerial signature and correspondence already agreed for issue by minister can issue under the Permanent Secretary.

It further advises that “purely factual” responses to correspondence can be issued, and where policy or political issues are raised, department should consider issuing a holding reply.

The note states that during the ministerial vacancy, the minster can have no access to their former departments, civil servants or papers, they should not be present in departmental accommodation, cannot use official transport and departmental press releases cannot carry any reference to previous remarks by the minister.

It also states that ministers’ special advisers become redundant when they leave office.

Meanwhile, it said the other departments, not impacted by the resignation of the unionist ministers, remain under the direction and control of their ministers.