Former Irish Nationwide chairman Dr Michael Walsh resigned after he brought in US investment bank Goldman Sachs to assist with a root-and-branch review of the building society.

The building society has refused to comment on suggestions that Walsh failed to win support from the rest of the board for his proposals.

Walsh, who had been chairman since 2001, wanted to appoint both a chief financial officer and a chief operating officer – standard roles in financial institutions – to assist long-term chief executive Michael Fingleton in the day-to-day running of the mutual.

However, after the board decided not back his plan, he chose to step down, according to informed sources. Walsh was not available to comment himself.

A spokesman for Irish Nationwide confirmed that Goldman had done work for the building society, but would not disclose the nature of that work. He said management had recently put forward a business plan of its own which the board accepted. It is understood this other plan did not include either a chief financial officer or chief operating officer.

Last month the Financial Regulator also reportedly recommended Irish Nationwide beef up its management with chief financial, operating and risk officers.