The 18th COSAC took place in London on 18-19 May 1998. The Presidential Troika had not been able to agree on a revision of COSAC rules and so the issue was not on the agenda of the London COSAC. Instead, COSAC deliberated on the current state of the enlargement of the EU, the Economic and Monetary Union (with particular emphasis on the independence of the European Central Bank), and scrutiny of Justice and Home affairs.
The Irish Oireachtas had tabled a proposal to enable extraordinary meetings of COSAC Chairpersons to be convened to ensure a higher frequency of meetings than the two annual conferences. But the proposal did not find approval among all delegations and was consequently rejected.
COSAC also discussed a proposal to change its Rules of Procedure in order to allow a representative of COSAC to participate in external meetings on behalf of COSAC and to report back to it. The proposal was dropped, however, because unanimity (required for any rule change) could not be reached.