The Taoiseach, Mr Ahern, is expected to travel to Belfast again early next week in an attempt to resolve continuing, and substantial, differences between the Ulster Unionists and the SDLP over North-South structures to be established under the Belfast Agreement.
Despite the goodwill generated by the British Prime Minister's historic address to the Oireachtas yesterday, informed sources last night said Mr David Trimble and Mr Seamus Mallon were continuing to "play hardball" over the remit of two proposed cross-Border implementation bodies - those concerning trade promotion and industrial investment, and EU programmes.
Mr Trimble is understood to have flatly rejected Mr Mallon's proposal for a powerful and highly significant implementation body covering trade promotion, business development and inward investment, which would involve the "harmonisation" of the activities of the Northern Ireland Development Board and the IDA.
And despite earlier indications of flexibility on the issue, Ulster Unionist sources last night insisted the party had not yet agreed on the creation of a 10-member executive to head the Northern Ireland Assembly.
Mr Mallon, the Deputy First Minister, and most other parties to the agreement expect a ministerial shake-up of the Northern Ireland departments which would result in three executive seats each for the Ulster Unionists and the SDLP, and two each for the DUP and Sinn Fein.
Sources close to Mr Trimble have indicated that the party would be prepared to move from its preferred seven to 10 ministerial portfolios, provided the new departments could be established "on a neutral-cost basis". That clawback on costs would presuppose a radical review of existing quangos and other statutory bodies.
But if the general expectation is that the Ulster Unionists will eventually shift their position on the proposed ministerial line-up, it seems clear the issue is being retained in the context of the continuing dispute with the SDLP about the extent of cross-Border co-operation on the trade and inward investment front.
Unionists are clearly hoping for Mr Blair's backing in their rejection of a scheme they say would require a harmonisation of corporate tax regimes on both sides of the Border - something they are confident would be unacceptable to the Treasury in London. They also argue that, apart from a loss of control of local enterprise initiatives, the SDLP plan "would erode Northern Ireland's political identity" and "cut us off from the UK business scene".
The Taoiseach will hope to persuade the unionists that it is possible to define a programme which would give Northern Ireland "the best of both worlds", as one Irish source put it last night.
Mr Ahern is expected to lead the search for a compromise on this issue, and to seek to resolve technical disputes concerning EU programmes, knowing that the effective deadline for overall agreement is next Thursday - the day before Mr Trimble leaves the North for a series of overseas engagements - if the two governments are to have time to effect the necessary legislation prior to the scheduled transfer of power to the Assembly next February.
Apart from these two, six other implementation bodies are expected to cover strategic transport and planning, tourism, waterways, food safety, aquaculture and marine issues, and language and culture.
Additional areas for North-South co-operation - to be effected through existing channels, and additional to some 140 areas already identified during the multi-party negotiations - include agriculture, animal health, teacher qualifications and exchanges, environmental protection, social security fraud control, accident and emergency services, rural and urban development, and inland fisheries.