The Oireachtas inquiry into a €45.7 million overshoot on a rail signalling system will reach the end of the line tonight when the subcommittee meets in private to discuss the text of an interim report. It is unable to make findings of fact in relation to the affair due to a High Court ruling but is expected to make a strong defence of parliamentary inquiries into the expenditure of public money.

With hearings suspended since last November, those close to the inquiry have no hope that the investigation can be completed before the general election.

The known costs of the inquiry to the Oireachtas are understood to be in excess of €1.27 million thus far. In addition, certain informed individuals are known to have expressed concern that the witnesses who figured in the hearings might challenge the State in the courts if no final report is produced by the inquiry.

The suspension followed a High Court judgment on an Oireachtas investigation into the shooting dead by gardaí of Mr John Carthy at Abbeylara, Co Longford, which restricted the scope of all parliamentary inquiries.

According to a number of figures close to the inquiry, there is little hope the Supreme Court will rule on an appeal to the High Court judgment in time to accommodate the completion of the rail inquiry before the Oireachtas rises. The Fine Gael public enterprise spokesman, Mr Jim Higgins TD, said: "It's obvious that we're not going to get back into business again but at least we'll have an up-to-date record on the proceedings."

Because of the High Court ruling, the interim report is unable to make conclusions about the evidence heard at 24 public hearings. When suspended, the inquiry was within one day of completion.

The inquiry sought to find out how the cost of a new signalling system on lesser-used lines on the Iarnród Éireann network rose to more than €63.5 million despite an initial projection of €17.78 million. Of the €14.6 million spent so far, more than €7.62 million was paid to consultants, internal and external.

The inquiry also sought to discover the value to CIÉ of a telecoms network laid along the railway by Esat group, the construction of which was said to have contributed, at least in part, to the overshoot.

It was unclear last night when the interim report would be laid before the Oireachtas.

According to informed figures, however, it was likely the interim report would reflect the view of the chairman, Mr Seán Doherty TD, who claimed when the hearings were suspended that the High Court ruling employed a "narrow and limiting view" of the role of parliament. "The courts have reserved to themselves an organic view of their powers," he said at that time. "I confess that I do not understand why the Constitution appears to mean one thing in Kildare Street and another in Inns Quay."

If the Supreme Court does not ease the restriction on such inquiries, observers believe an amendment to the Constitution will be required to enable politicians to conduct similar inquiries.