The investigation by the two inspectors appointed to National Irish Bank is to be held up once again following the decision yesterday by a group of managers and senior executives to appeal their right to silence case to the Supreme Court.

Earlier this month, the High Court ruled that the managers and executives must answer questions put to them by the inspectors, the former Supreme Court judge, Mr John Blayney and Mr Tom Grace.

The approximately 130 former and serving staff who took that case have now decided to appeal the decision to the Supreme Court. Legal sources said it was likely the inspectors would seek to have the appeal heard in October.

They also said that if the Supreme Court decision went against the NIB staff, the option of taking the case to the European Court of Human Rights in Strasbourg would then be considered. Such a course of action would hold up the investigation for two to three years.

The bank has said in the past it would support staff in relation to legal costs incurred by them as a result of the various investigations into the bank.

The decision of the High Court was considered a victory for the inspectors and the public interest. As it confirmed the extensive powers of inspectors appointed under the Companies Act 1990, it was of relevance to all future appointments under the Act.

The inspectors had hoped to begin interviewing the staff in May but were prevented by the initiation of the High Court case. The staff wanted the right to refuse to answer questions which might incriminate them or be used in evidence against them in subsequent criminal proceedings.

They also wanted the High Court to dictate certain procedures which would have to be followed by the inspectors, including the right to attend the interviews of other witnesses and to cross-examine them.

However, the High Court ruled that the obligation to answer self-incriminating questions was not inconsistent with the right to trial in due course of law.

Whether or not there was a constitutional right not to have compelled testimony used against an accused was an issue which the court felt it did not have to rule on as it had not yet arisen. The court also found that the procedures proposed by the inspectors regarding the interviews were consistent with the requirements of constitutional and natural justice.