The courtroom challenges, which resulted in two separate High Court hearings last week, are the first major tests of ombudsman Joe Meade's powers to adjudicate in disputes between financial institutions and their customers.

He was appointed last year as part of a government push to give consumers a stronger hand in dealing with financial institutions, and handled more than 2,600 complaints in his first nine months in office.

Last Monday, the High Court gave permission to Ulster Bank to appeal Meade's decision that the bank should pay substantial compensation to savers who lost an estimated 5m in 2004 after investing in Ulster's international share portfolio.

The size of the award has not been disclosed, although it is understood that 480 people lost an average of 10,000 each after the value of the fund had to be written down.

On Tuesday, lawyers representing the ombudsman were back in the High Court, pledging to fight an application by Irish Nationwide Building Society for a judicial review aimed at quashing a 30,000 refund Meade ordered it to pay to one of its mortgage customers. Within days of the initial application by the Irish Nationwide, the chairman of the ombudsman's council, Con Power, resigned as a director of the building society.

It is understood Meade ruled in favour of the Ulster Bank customers last month after they had complained about a shock 14.6% writeoff in the value of their 30m investment, triggered by poor investment performance and an exodus of money from the fund. The ombudsman awarded them substantial compensation, even though the write-off was allowed by the rules of the investment fund and approved by its trustees.

The challenge mounted by the Irish Nationwide is potentially more serious because it calls into question the considerable powers the ombudsman has been granted by the government.

The building society is seeking to block Meade's order that it should repay 30,000 of a 74,000 penalty charged to John Scully of Roagstown Golf and Country Club in Swords, Co Dublin. He had taken out commercial mortgages from the Irish Nationwide in 1998 and 2000 and was penalised when he repaid the loans early in 2003.