Ian Paisley jnr's decision to resign as junior minister in the Northern Executive has raised serious questions about how long his father can remain as First Minister and leader of the DUP.
Mr Paisley jnr announced his resignation at Stormont Castle yesterday after he was instructed by members of the DUP leadership to "reflect" on his position over the weekend, following a series of embarrassing and damaging revelations about his political and business dealings.
DUP sources acknowledged yesterday that the "succession" is now a live issue within the party. While Dr Paisley has previously insisted he will see out his full four-year term in office, some sources suggested he would step down as leader and First Minister by the summer or early autumn.
A series of disclosures about Mr Paisley jnr's relationship with prominent north Antrim businessman Seymour Sweeney, along with other matters, prompted his statement in which he adamantly denied being involved in any misconduct.
"I cannot express strongly enough that I am not going because of some hidden or some revealed wrongdoing on my part," he said. He complained of being subjected to "personal criticism, unfounded allegation, innuendo and attacks" on him personally.
Mr Paisley, who is to remain as an Assembly member for North Antrim, became embroiled in controversy last September, which has rumbled on ever since, over his lobbying on behalf of Mr Sweeney who was seeking to build a visitor centre on land he owns beside the Giant's Causeway.
While Mr Paisley jnr initially tried to downplay the extent of his relationship with Mr Sweeney, it quickly emerged he had lobbied on the businessman's behalf on several occasions, that Mr Sweeney was a DUP member, and that he had bought a house from Mr Sweeney.
While there have been no allegations of any illegal activity, the continuing publicity surrounding Mr Paisley caused deep unease within the party.
Senior members were angry when MEP Jim Allister disclosed through a freedom of information request that Mr Paisley had lobbied British prime minister Tony Blair about a number of issues, including the Giant's Causeway visitor centre and a multi-million land deal at Ballee near Ballymena in which Mr Sweeney was involved.
DUP negotiators said they were unaware of this lobbying, which happened on the margins of the St Andrews talks in October 2006.
In recent weeks there was further bad publicity with the revelation that while being paid almost £63,000 (€84,460) as an MLA and junior minister, he was also being paid as a Westminster researcher for his father.
The issue that may have finally sealed his ministerial fate was the disclosure at the weekend that he and his father had paid £42,000 (€56,300) from the public purse to rent a constituency office in Ballymena, a sum that was viewed as strikingly high.
It emerged that Mr Sweeney had been a director of the firm that rented the property and that the current sole director is the father-in-law of Mr Paisley.
Some DUP sources said Dr Paisley might remain as First Minister to host with Deputy First Minister Martin McGuinness the special economic conference in May, to which leading US business leaders are invited.
They expected that in the weeks or months thereafter Dr Paisley would resign.
The effective forced resignation of his son is a huge personal blow to Dr Paisley, who for a considerable period of the Assembly sitting yesterday sat alone on the DUP front benches.
