The allegations were made in a BBC Spotlight programme
Police in Northern Ireland have launched a criminal investigation into the financial dealings of former DUP Strangford MP Iris Robinson.
A BBC Spotlight programme said she acted illegally over money deals connected to a business being run by a man with whom she was having an affair.
The investigation will be carried out by the organised crime branch.
The programme said she obtained £50,000 from property developers for a business venture for her 19-year-old lover.
It was alleged that she failed to register the money, from two developers, at Stormont or Westminster, and that when her husband Peter Robinson, Northern Ireland's first minister, found out about the money, he failed to alert the authorities.
Mr Robinson has denied any wrongdoing. He announced last week he was stepping down temporarily from his duties as Northern Ireland's First Minister to clear his name.
Since the programme was broadcast, Mrs Robinson has resigned as an MP and member of the Stormont Assembly.
In a statement on Thursday, a police spokesman said: "Police can confirm that a criminal investigation has been launched into allegations made in a BBC Spotlight programme broadcast on 7 January 2010.
"The investigation will seek to establish whether any criminal offence has been committed by Iris Robinson, MP, MLA and by any other person referred to in the programme.
"The investigation is led by Detective Chief Superintendent Roy McComb who is head of the Police Service's Organised Crime Branch, which specialises in complex financial investigations.
"The police service is aware of the substantial public interest in this investigation. The police remit is to investigate potential criminality, nothing else. Police will be making no further comment on the investigation at this time."
The Northern Ireland Assembly's Committee on Standards and Privileges had
begun an inquiry into the conduct of Iris and Peter Robinson.
However, it is understood that the police investigation is likely to delay this inquiry.
Such a delay is not unprecedented - when Mrs Robinson was being investigated by police over her remarks about homosexuality being "an abomination", the committee delayed that inquiry.
Ultimately, it will be a matter for the Assembly's Ombudsman Tom Frawley to make the recommendation to the committee on how to proceed.