The council is to look into Iris Robinson's behaviour as a councillor
The BBC understands Castlereagh Council has asked consulting firm Deloitte to investigate allegations surrounding Iris Robinson and the Lock Keepers Inn.
Details have not been formally declared, but the council is due to make an announcement shortly.
The council is expected to declare that Deloitte will carry out the inquiry.
The inquiry will examine whether the council suffered financial loss by awarding the lease for the cafe to Mrs Robinson's lover, Kirk McCambley.
Castlereagh councillors set the remit for the investigation on Wednesday.
They want the enquiry team to examine if any impropriety has taken place, if the council has lost any money and if legislation was broken.
Meanwhile at Stormont, assembly members agreed to contact Environment Minister Edwin Poots to ask what role his department would have following the allegations broadcast in the BBC's Spotlight programme.
Mrs Robinson procured money from two developers to help Kirk McCambley to open the cafe.
She then attended a council meeting when the lease was awarded and broke the law by not declaring an interest.
Investigators will be also be asked to ascertain whether or not council officers and members complied with local government legislation and to examine if any impropriety took place.