The decision by Iris Robinson to quit politics because of a battle with mental illness shocked her Democratic Unionist Party.
Some of Iris Robinson's closest associates, including a number of MPs, were unaware of her plans to withdraw from public life until she made the announcement, according to party sources.
"It came right out of the blue," said one. "Hardly anybody had advance warning this was going to happen."
A meeting of the party officers will be held to discuss the decision, possibly later this week.
It expected she will stay on as MP for Strangford until the general election next year, but her position at the Northern Ireland Assembly where she was once chairperson of the health committee, is likely to be filled as soon as possible.
It is understood she had been away from her desk for a period earlier this year, and after talking about her future at Stormont and Westminster with her husband over Christmas, decided she needed to stand down.
In a statement to the Press Association last night Mrs Robinson, 60, a mother of three, and an MP since 2001 said she had suffered serious bouts of depression. She added: "The stress and strain of public life comes at a cost and my health has suffered."
Northern Ireland Secretary of State Shaun Woodward paid tribute to her work as an MP.
Mrs Robinson has been at the centre of two major controversies this year - her criticism of homosexuals and revelations that she and her husband who is also MP for east Belfast draw more than £500,000 a year in salaries and expenses, which includes payments to four members of the family who work on their staffs.
She provoked outrage among the gay community when she claimed homosexuality was an abomination which made her feel sick.
It caused uproar, and she was labelled "Wicked witch of the north". But despite the fierce criticism, Mrs Robinson remained defiant.
In her statement last night she said she had recently tried to return to the full-time work of representing her constituents following the latest period of illness.
She added: "Over the years, I have undergone a long series of operations and though I have never talked about it publicly, I have, against this background, also battled against serious bouts of depression.
"Only those who have faced similar challenges in life will know the ordeal faced by those who are profoundly depressed and the distress caused to those around them as they grapple with personality changing illness.
"One in four of the population struggle with mental illnesses at one level or another yet few talk about it openly.
"When I am better able to do so, I want to say more about this period of my life.
"The stress and strain of public life comes at a cost and my health has suffered. Regrettably I have concluded, after considering the matter over Christmas and discussing it with Peter, who has always been most supportive and caring, that I can no longer maintain the high standard of service I require of myself, meet the demands of office and cope with the pressures of public life without my health deteriorating yet further."
The resignation statement in full
“In order to make progress with the selection process for the Westminster general election the party officers asked each of its MPs to advise them of their intentions.
“As many people will be aware I have recently tried to return to the full-time work of representing my constituents following my latest period of illness. Over the years I have undergone a long series of operations and though I have never talked about it publicly, I have, against this background, also battled against serious bouts of depression.
“Only those who have faced similar challenges in life will know the ordeal faced by those who are profoundly depressed and the distress caused to those around them as they grapple with personality changing illness.
“One in four of the population struggle with mental illnesses at one level or another yet few talk about it openly. When I am better able to do so I want to say more about this period of my life.
“The stress and strain of public life comes at a cost and my health has suffered. Regrettably I have concluded, after considering the matter over Christmas and discussing it with Peter, who has always been most supportive and caring, that I can no longer maintain the high standard of service I require of myself, meet the demands of office and cope with the pressures of public life without my health deteriorating yet further.
“I have always considered it an enormous privilege to serve the people of Strangford and it has been a most rewarding and satisfying experience. I do not intend to seek re-election to public office and will discuss with party colleagues how best to effect a smooth and seamless transition.
“It has been an immense honour to serve the people of this constituency in various elected roles since 1989 and as MP since 2001. I cannot begin to explain how much I have genuinely and thoroughly enjoyed meeting with, and working for, the people of Strangford.
“Having inherited a constituency that had no significant advice centre network we have worked hard to build up the service that is now available to the area.
“I am proud to have been part of a team that now consists of not only a Democratic Unionist MP, but four Assembly Members and a massive team in local government.
“It has been gratifying to see the substantial increase of support for the party in the constituency since I first stood. I was particularly pleased that the returns from the European election count showed the DUP still comfortably topped the poll in Strangford.
“I want to take this opportunity to thank all those who voted for me at each of the elections as well as the many thousands who stood by me during difficult and sometimes controversial periods. At all times in public life I have tried to do what I believed was in the best interests of those whom I served.
“I will, of course, continue to take a keen interest in politics and give full support to my husband and the party he leads.”
CONTROVERSIAL VIEWS OF DUP WOMAN
Outspoken MP Iris Robinson has seen her career dip in the last two years as she became one of the DUP's most controversial figures.
From the highs of winning and retaining her Westminster seat in 2001 and 2005, the Strangford representative's image was badly damaged by her comments about gay people.
A born-again Christian, the 60-year-old sparked a wave of criticism after claiming on live radio that homosexuality was an abomination that made her feel sick.
It earned her the titles of "bigot" and "wicked witch of the north".
And the timing of her comments in June 2008 could not have been worse - she spoke out 24 hours after gay man Stephen Scott was beaten by three men near his home in Newtownabbey, Co Antrim, in an unprovoked attack.
Her husband and First Minister Peter Robinson was only in his new job a few days when she spoke out.
Less than two months after the outburst, an online petition calling for Prime Minister Gordon Brown to reprimand Mrs Robinson gathered 16,000 signatures.
Amnesty International and the Labour Party were among the many groups calling for action against the Strangford Democratic Unionist.
Mrs Robinson, a member of the Metropolitan Tabernacle Church in Belfast, went on to defend her remarks claiming she aired them in the wrong environment before saying "love the sinner, not the sin".
During the radio show, the MP also suggested one of her advisors, a consultant psychiatrist, was available for homosexuals to talk to, before adding: "I have met people who have turned around and become heterosexuals."
Dr Paul Miller later resigned from his role with Mrs Robinson and also stood down from his post as a consultant psychiatrist in Belfast's Mater hospital.
A police investigation examined claims her comments breached hate crime laws but no charges were brought.
Following the scandal, gay rights group Stonewall voted her the UK Bigot of the Year 2008 while the gay news service Pink News landed her with the wicked witch nickname.
The First Minister, whose office is charged with promoting equality, subsequently endorsed his wife's views insisting she was following the teaching of the Bible.
A mother-of-three, further controversy followed earlier this year when the Westminster MPs expenses scandal broke.
Records showed the Robinsons received more than £500,000 a year in salaries and expenses while a further £150,000 in wages was being paid to four relatives - including daughter Rebekah and son Gareth - for constituency and other work.
The payments earned another nickname - "Swish family Robinson".
But despite the criticisms and embarrassments, Mrs Robinson showed little signs of the strains of public office during one of her last one-to-one interviews about two months ago.
Insisting she did not think she could ever retire, the Strangford representative, who wrestled the seat from Ulster Unionist control in 2001, said she feared ageism might play a part in future elections.
She went on to claim there would be good times ahead and that she loved her work.