SDLP MLA Conall McDevitt is to quit politics with immediate effect following a row over earnings he did not declare.
Mr McDevitt had been the managing director of the company, but quit to move into politics and was elected to succeed the SDLP's Carmel Hanna in 2010.
He said on: "I have submitted by resignation as an MLA with immediate effect.
"Over the past few weeks there has been considerable public interest in my use of public money.
"I am satisfied that at all times I complied with the obligations on me and am compliant with my duties.
"Between March 2010 and August 2010 I received a total of £6,750 from my former employers, Weber Shandwick. These payments related to internal work within Weber Shandwick. I resigned as Managing Director of the Belfast office in December 2009 and I provided support and mentoring to the new management team following my departure from the company.
"I was never asked to nor did I ever represent any of the company’s clients whilst an MLA. These payments were made through JM Consulting, a consultancy which my wife has an interest in. These are registerable interests under the Assembly rules. I have now registered these earnings on my register.
"My failure to register these interests at the time means that I have fallen below the standards of expected of me in public office.
"I have done my best to discharge my duties as an MLA with integrity but there is no question that I failed to do so on this occasion.
"I apologise unreservedly for my failures in this regard. It has been the greatest honour of my professional life to serve the people of South Belfast and the SDLP since January 2010.
"I will forever treasure the opportunity given to me to make a contribution to the building of a new society here.
"That work will be continued by my successor whomever he or she may be.I would like to ask for some privacy at this time for myself and my family."
SDLP Leader Dr Alasdair McDonnell confirmed he had accepted Conall McDevitt's resignation.
He said in a statement: “Conall McDevitt has done the right thing by resigning after admitting his failure to register funds received by him during his time as MLA in accordance with Assembly rules.
“I welcome Conall’s speedy and definitive response in this regard and accept his resignation. As elected representatives we quite rightly hold ourselves and are held by the electorate to a very high standard.
“South Belfast was very well represented by Conall McDevitt and he made a very positive contribution not only to the constituency but also to the wider SDLP party where he showed energy, enthusiasm and drive. Conall will be a loss to the Assembly party and to South Belfast and I would like to wish him and his family all the best for the future.”
Payments to wife
On Tuesday the Belfast Telegraph revealed that Mr McDevitt admitted his wife, Joanne Murphy, received £30,000 in public funds in the last two years, carrying out research for him in his role as a member of the Northern Ireland Policing Board.
Conall McDevitt paid the money directly to his spouse Dr Joanne Murphy – an academic and policing reform expert – for the past two years.
But the South Belfast MLA insisted the payment was "completely above board" and declared in the board's annual report.
However, the report does not name Mr McDevitt or another board member who also declared employing a close family relative as a researcher.
Mr McDevitt explained he took legal advice and was told he did not need to include the Policing Board allowance in the Assembly Register of Members' Interests.
And he further revealed that former party leader Margaret Ritchie gave him permission to engage his wife in the research work.
He insisted: "There is no secrecy here.
"The rules allow me to do this and even if she were not my wife, I would still want her because she is an expert in this area.
"I thoroughly checked the matter out and I am not required to declare that in the Assembly register.
"This is entirely separate from my office cost allowances, and in my view it demonstrates that I have complied with all the codes and rules."
Mr McDevitt, who replaced Dominic Bradley on the board in 2011, also said he wanted to make clear that his wife's research – including her recent book Policing For Peace – did not involve any information she had gleaned as part of her work for the Policing Board.
Dr Murphy, a lecturer in Queen's University's management school, also wrote Embedding The Peace Process in 2010 and Policing Change in 2011. Mr McDevitt said she had also included her Policing Board work in the register of interests at Queen's.
DUP Policing Board member David McIlveen said that while his behaviour was within the rules, "I do not think it is good form to be doing that, and he should certainly have been more sensible".
He added: "I think if this is going to embarrass the board it will definitely have to be looked at.
"There have been concerns that standing orders are a bit loose in the way they are operated.
"There is a bit more discretion over Assembly allowances and I have some sympathy with elected representatives using family members who they can trust, but less so with an outside body like the Policing Board."
An Assembly statement said: "All Members are required to register family members who benefit directly or indirectly in any way from the Assembly's office cost expenditure.
"MLAs are aware that there is no requirement to register family members who benefit from allowances or expenses arising from any other public office."
The latest controversy came after it emerged earlier this summer that Mr McDevitt had claimed more than £14,000 for research and secretarial work paid to four academics through his wife's firm.