Northern Ireland First Minister Peter Robinson last night vowed to clear his name after denying any knowledge of his wife's irregular financial dealings with her teenager lover.

The Democratic Unionist leader ordered an official inquiry into his conduct on discovering his MP wife Iris had secured £50,000 from two wealthy developers to help her 19-year-old toyboy set up a restaurant business in south Belfast.

As well as the illicit affair, he claimed she had also concealed the nature of the donations she obtained.

"I had no information," he said.

"Absolutely no information about that, nor of any of the other financial arrangements, which is hardly surprising if somebody is hiding an affair from you, it's probably not a surprise they are hiding the other arrangements relating to that affair."

The East Belfast MP faced calls to resign or consider his future amid heightening unease and deep disquiet within his own ranks following claims that he failed to alert the authorities that Mrs Robinson did not declare her monetary interest in her lover's Kirk McCambley's restaurant - even though she was a member of the council that gave him the go-ahead to open in 2008.

Already under pressure from rival unionists going into the general election, some senior DUP members fear the leader might not survive this crisis and the sex and money scandal involving his troubled wife. She is quitting politics because of severe depression and has not been seen since Christmas.

Mr McCambley, 21, refused to comment at his business on the banks of the River Lagan.

But Mr Robinson came out fighting tonight, ordering civil servants to call in senior lawyers to probe his actions.

Adamant he did nothing wrong, he admitted there would be consequences for his position as First Minister if the legal experts found otherwise.

At the office of the DUP headquarters in his East Belfast constituency he told the Press Association: "I have consistently indicated that I have done nothing wrong, that I acted properly.

"But me believing that and saying it in my view is not sufficient because I am being, if you like, tried by the press and therefore I think that we need to have an investigation."

Asked what he would do if the lawyers did find he had breached ministerial codes, he said: "If there is (a breach) I will have to clearly and publicly indicate that is so and that clearly will mean there are consequences that I have to consider ... in regard to my position."

Tonight it emerged that Mr Robinson's partner at the head of the powersharing government, Sinn Fein's Martin McGuinness, has also requested that officials seek legal opinion on the allegations.

The scandal has broken with the Executive already destabilised by the ongoing rift between the DUP and Sinn Fein over delays in devolving policing powers to the region.

A Sinn Fein source said: "Martin McGuinness is very concerned by the issues raised in last night's (television) programme. This morning he requested a legal opinion to be prepared by the departmental solicitor's office concerning any implications for the operations of the OFMDFM."

The source said Mr McGuinness also contacted the Irish and British Governments today to raise concerns about the policing.

Strangford MP Mrs Robinson issued a statement this week admitting the affair and revealing that, wracked by guilt, she had tried to take her own life in March last year.

But last night a TV documentary added explosive claims not only about the nature of her sexual relationship with Mr McCambley, but also on her financial dealings with him.

Though conceding his wife's "irrational behaviour" had caused embarrassment, Mr Robinson said he had been kept in the dark about the nature of the £50,000 when he found out about it December 2008.

As far as he was concerned, she was simply trying to get a young man to pay back money he owed to two developers.

He said when he discovered she intended to get the money returned through her initially, he said he insisted it was given directly to the developers through solicitors.

The DUP leader said many of the details outlined by the BBC Spotlight Team - namely her role in the business and her failure to declare it - were not known to him at that time.

He therefore had no reason to report his wife to the authorities, he claimed.

"There were elements of the Spotlight investigation that came as a shock to me," he said.

"There were matters that I had not heard about before, detail in relation to my wife's affair that I had not been aware of, matters relating to the financial arrangement about which I knew nothing."

Asked whether the fact his wife's lover was just 19 when she started the affair had added to his sense of hurt, the First Minister replied: "I don't think it has any impact on the scale of pain or hurt anybody feels as to who it is, the sense of betrayal is still as great."

Mrs Robinson and Mr McCambley, now 21, first became close after she comforted him following the death of his father, Billy, an east Belfast butcher who was a family friend. They started a sexual relationship in the summer of 2008.

But the affair ended in acrimony that winter after the couple rowed over the repayment of the money.

The documentary claimed that earlier that year, Mrs Robinson had encouraged the teenager to bid for the tender to run a cafe at the historic Lock Keeper's Cottage, a site Castlereagh Council was redeveloping.

She then obtained two £25,000 payments from the developer Fred Fraser, who has since died, and Ken Campbell.

According to the programme, at the time Mrs Robinson was asking Mr Campbell for the money, she also lobbied on his behalf for one of his building projects in her parliamentary constituency of Strangford.

Mr McCambley told the documentary both cheques were made out in his name but that Mrs Robinson asked him for £5,000 back in cash. The council subsequently awarded him the contract to run the cafe.

However, it is claimed Mrs Robinson failed to register her financial interest in the scheme to her fellow councillors.

She also faces claims that she did not record the two loans on her declaration of interests at Stormont and Westminster.

Castlereagh Borough Council today launched an investigation into the issues raised by the documentary.

Although Mr Fraser and Mr Campbell were family friends, Mr Robinson said the first he heard about the money was when his wife was attempting to get it paid back while on a family holiday in Florida.

"By the time I heard one of those friends had died the other has indicated to me that he was approached much on the basis that this was someone she was helping following the death of his father, that he deserved a chance in life and was he prepared to give some assistance to start him up in business and the cheque was made out directly to the individual concerned and also that this was a matter between themselves."

The First Minister also denied knowledge of the £5,000 cash payment his wife had allegedly taken from the original £50,000.

He went on to accuse the media of attempting to draw him into the issue on the basis of innuendo and did not rule out taking legal action.

When asked whether he believed his wife should have declared an interest in the business, he said: "I am not going to step in and usurp her legal rights."

The DUP leader revealed that his wife was too unwell to even answer the allegations levelled at her.

"I am not even in the position where I can question my wife about these issues," he said.

"Neither her solicitor or I would be confident about the responses we are getting to any questions."

The MP also hit out at any suggestion that his wife was overstating the seriousness of her illness.

"To listen to some people you would get the impression that Iris has really no mental difficulties and this was all a bluff to cover the problems she is facing," he said.

"This is someone who had a breakdown, has had treatment in a clinic in which she was there on two occasions for six to eight weeks and who has to this day been receiving psychiatric help.

"I have to say that though I have been hurt by many of the things she has done both in terms of financial arrangements and in terms of the affair, I have to say it is a bit hard to take the suggestion that somebody who would attempt to take their own life is in some way bluffing in these matters."

Mr Robinson said he was calling for the legal opinion because any potential defamation case would take years to complete while expected probes by parliamentary watchdogs would take months.

"In the Office of First and Deputy First Minister I think it needs to be seen that I have acted properly and that any question needs to be removed," he said.

In regard to a possible defamation writ, he said: "I am being tried by media and the court of public opinion and therefore I can't wait for the outcome of such an engagement."

Mr Robinson admitted it has been a traumatic experience to see his family life so publicly laid bare.

"I think you can imagine that I have been deeply hurt and affected by the issues," he said.

"I think it's difficult for anybody to have to cope with the aftermath of finding out your partner in marriage has had an affair.

"I have had to do it in a very public way and also had to do it in context where her irrational behaviour has clearly been carried out in way that has caused embarrassment."

Ulster Unionist Party (UUP) leader Sir Reg Empey said Mr Robinson should consider his position as First Minister.

"The prospect of a plethora of inquiries going on for months, distracting the First Minister and leaving Stormont in a powerless state, cannot be contemplated," he said.

"The UUP therefore believes that Peter Robinson should give very serious consideration to his own position as First Minister.

"The country is crying out for leadership at a time when we are encompassed by terrorism on the one hand and a stalled Executive on the other - he is not providing that leadership."

Following a meeting of the DUP officers in Stormont last night, a spokesman said: "The party officers have accepted Iris Robinson's decision to step down from political life.

"The party will consult with the Strangford DUP association and fill the vacated Assembly seat as well as setting in place processes to deal with the council and Westminster situations."