Sinn Fein have mounted a legal bid to have Northern Ireland Secretary Mr Peter Mandelson brought before the High Court as it battles to block the union flag being flown at ministerial offices.
A judicial review brought by the party is seeking to overturn Mr Mandelson's ruling that the flag must be hoisted at government buildings on specified days throughout the year.
An application by Sinn Fein's legal team was lodged with the High Court in Belfast before the close of business seeking permission to cross-examine the Secretary of State about an alleged deal he struck with Ulster Unionist Party leader Mr David Trimble.
They have also requested disclosure of any further documents which may shed more light on claims that the flags legislation was implemented last year in return for the UUP returning to the power-sharing administration.
The judicial review has been adjourned until Monday when Mr Justice Brian Kerr will consider the application to subpoena Mr Mandelson.
As it stands the union flag must be flown on 17 designated days outside government offices including the departmental buildings of Sinn Fein Education Minister Mr Martin McGuinness and his party colleague, Health Minister Ms Bairbre de Brun.
The legal challenge was brought by Sinn Fein Assembly member Mr Conor Murphy on the basis of "political interference" by Mr Mandelson.
Mr Seamus Treacy QC, for Mr Murphy, today told the court that correspondence between Mr Trimble and Mr Mandelson indicated the Secretary of State's intervention was crucial to ending the suspension of fledgling political institutions at Stormont last May.
Two affidavits were lodged on behalf of Mr Mandelson, the second of which included a letter indicating he had been approached by the UUP on the flags issue.
The Secretary of State insisted the flags order was not the result of an agreement with the UUP, Mr Treacy said.
But he drew Mr Justice Kerr's attention to a letter from Mr Trimble to Mr Mandelson on July 21, 2000 which highlighted "the sensitivity of this issue to the majority community in Northern Ireland".
The correspondence also noted that resolving it to the Ulster Unionists "satisfaction" had helped Mr Trimble recommend a return to devolved government to his party, Mr Treacy added.
"There had been an agreement reached between the Ulster Unionist Party and the British Government and part of that agreement included a commitment by the British Government on the flags issue," he said.
Speaking about the disclosure of any further material available on the matter from Mr Mandelson he said: "There must be other documents apart from that single letter on this very important issue."
Mr Ronald Weatherup QC for Mr Mandelson rejected any implications that there was "some kind of secret" involved.
He said the Secretary of State wrote to Mr Trimble on May 15th setting out that he was addressing the flags issue and concerns raised by unionists.
That letter was then published in The Irish Times.
Mr Weatherup added: "This idea that this document is something that they were not aware of is not accepted. The matter has been in the public arena."
PA