Parliament Buildings at Stormont required “substantial structural alterations” to prepare it to host the newly-established devolved Assembly, ministers were warned in 1998.

Newly-released state papers show that officials also considered using Castle Buildings in the Stormont estate, pointing out that less work would be required because of the “prevalence of stud walls”.

After the signing of the historic Good Friday Agreement in April 1998, civil servants’ attention quickly turned to preparatory plans for a new political body.

A DoE memo sent in April from civil servant Felix Dillon to NIO ministers Lord Dubs and Paul Murphy set out the options.

It said: “Office Accommodation Branch (OAB) has been assessing the options for the location of a new political body immediately based on a notional specification of requirements requiring a gross floor area of 3500m squared.

“This assessment has concluded that only Parliament Buildings and Block B, Castle Buildings (supplemented by other accommodation in Block A) represent practicable options.

“It has been assumed for planning purposes that ministers will wish to avoid overt preparations for accommodating the new political body until the outcome of the referendum is known.

“Nevertheless a decision on location is required within the next few weeks to provide maximum planning time.

“Whatever location is chosen for a new political body there will be only five weeks from the referendum to complete any necessary decanting and preparatory work.”

Regarding Parliament Buildings, the memo stated: “To meet the assumed accommodation requirements in full would necessitate substantial structural alterations.

“Lack of time, the uncertainty of needs and the fact that the building has been recently refurbished all mitigate against this.

“Room sizes will therefore be constrained by the current configuration of the building and consequently space will be allocated to the various purposes on a best fit basis.

“For a 108-member political body, the Commons chamber is capable of being laid out in a number of different configurations although not all options would provide space for distinguished visitors or the provision of seating with desks.

“A basic chair and shelf layout without tiers could be provided very quickly with the final resolution of the seating configuration left to the political body to decide.”

The paper said that at Castle Buildings, “any adjustment required would be a relatively simple task because of the prevalence of stud walls”.

Minutes of an inter-departmental meeting the following month with Northern Ireland parties on progress towards a local administration, stated that discussions had taken place on the location of the Assembly.

It said: “The only outright opposition on using Parliament Buildings had come from Sinn Fein, with the SDLP declining to offer a strong view.

“The Secretary of State (Mo Mowlam) and Mr Murphy will decide within the next few days whether to consult further or to make their own decision on where parties should locate.”