A Belfast court has upheld a ruling that former first minister David Trimble's ban on Sinn Fein ministers attending meetings of the North-South Ministerial Council was illegal.

Although he has since resigned as first minister, Trimble imposed the ban in November 2000 as he sought to pressure the IRA into decommissioning their weapons. Sinn Fein sought to overturn the decision in the courts, and in January Mr Justice Kerr ruled that Trimble had acted unlawfully in preventing health and social services minister Bairbre De Brun and education minister Martin McGuinness from attending the meetings.

In a Belfast Appeal Court ruling on Friday Lord Chief Justice Carswell upheld the earlier decision, having said in in June, when judgement in the case was reserved, that there were "difficult and delicate issues to consider''.

Lawyers representing the former first minister had argued that the discretion available to the first minister permitted him to make the decision. However, the judge said the reasoning in introducing the ban to pressure the IRA was not acceptable.

The judge ruled that the aim of the Northern Ireland Act was to foster north-south links through the council and therefore Trimble's ban "cannot be sustained as a valid exercise of that discretionary power".

The North-South Ministerial Council is one of the most important aspects of the Good Friday Agreement for nationalists. Its purpose is to encourage cooperation between Northern Ireland and the Republic of Ireland in areas of mutual concern.

The latest ruling comes the day after Mr Justice Kerr ruled that then Northern Ireland minister Peter Mandelson had acted lawfully in ordering that the Union flag should be flown on public buildings on 17 elected days.