The Northern Secretary could face courtroom questions over Sinn Fein's claim that he did a secret deal with unionists. The deal is alleged to have concerned the flying of the Union flag at government buildings.
The prospect of Mr Peter Mandelson in the witness box was disclosed in the High Court in Belfast yesterday when a lawyer gave notice of an application to cross-examine him. Mr Justice Kerr said he would deal with the application on Monday.
A Sinn Fein Assembly member, Mr Conor Murphy, is seeking a judicial review of the Flags Order brought in by Mr Mandelson. Under this, the Union flag must be flown on 17 designated days at government offices, including those of the Sinn Fein Ministers, Mr Martin McGuinness and Ms Bairbre de Brun.
Sinn Fein says the order is against the spirit of the Belfast Agreement and wants the Irish Tricolour flown alongside the Union flag, or no flags at all.
The party claims Mr Mandelson did a deal with the Northern Ireland First Minister, Mr David Trimble, so Mr Trimble could get the backing of the Ulster Unionist Council last May.
Mr Ronald Weatherup QC, for Mr Mandelson, said his client "wholly rejected" the implication of some kind of secret deal. He indicated the application would be opposed.