He said he was disappointed to miss out on the role, awarded to Simon Allen, as he believed it would have "allowed me to continue to serve the New Zealand public in a way that I believed made best use of my skills and experience."

Mayhew said he would step down from his role on April 30 or earlier, depending on the establishment of the Financial Markets Authority (FMA).

Mayhew said that in his judgement, "the substantive work of the Commissioner will be completed by April and the remaining work can be subsumed by the FMA as soon as it is established."

Power said, "I'd like to thank him for the significant contribution he has made to the financial services industry and in helping pave the way for the introduction of the FMA."

In his resignation letter Mayhew said the implementation of the Financial Advisers Act (FAA) regime was well under way.

"By the end of March, the Commission will have granted Qualifying Financial Entity (QFE) status to those financial service firms who have applied; and the licensing regime for AFAs will be in full swing," he said.

"What will remain will be essentially executive functions that will fall to the CEO of the FMA to take forward with the support of the current Securities Commission FAA team."

He said the Disciplinary Committee would be unlikely to have to hear any complaints before the end of the year as none had been received to date.

Considerable lead time is required to develop a disciplinary load case, and in the meantime, "rules to regulate the procedure of the Disciplinary Committee will be approved by  the Committee in the next month or so."

Mayhew was appointed to the role back in January 2010 to oversee the drafting, approval and implementation of the Code of Professional Conduct for Authorised Financial Advisers (AFA).

The Code outlines the minimum standards of competence, knowledge and skills, ethical behaviour, client care and professional training requirements that AFAs must comply with and came into effect on December 1, 2010.

He said it has been a privilege to hold the role of Commissioner for Financial Advisers during the challenging time of designing the new regulatory framework and that he intended to return to London to seek consultancy work.

"I will continue to follow developments in New Zealand and, should an opportunity arise in the future where you think I might be able to assist in that capacity, I would be happy to consider it."