Pressure has grown on the DUP to reveal if it ever received money from the late property millionaire Fred Fraser.
The issue has arisen after it emerged Mr Fraser helped finance the new café business of Iris Robinson's teenage lover in 2008.
Sir Alistair Graham — one of the UK's leading public standards experts — has urged full disclosure from the party led by Mrs Robinson's First Minister husband.
The DUP has so far not responded to Belfast Telegraph queries on whether Mr Fraser provided it with any financial support.
Sir Alistair, former chair of the Committee on Standards in Public Life, the UK's official anti-sleaze watchdog, said: “Given the importance of transparency about donations, the DUP should provide answers on this matter.”
He also backed calls for an end to the secrecy surrounding donations to all political parties here.
Parties in Britain and the Republic are required to disclose details of financial backers. Northern Ireland, however, remains exempt from UK transparency legislation introduced in 2001.
Sir Alistair said: “Now that life is to some extent returning to normal and given all the questions about the operation of the political system, there should be no exemption for Northern Ireland.”
The lack of transparency has been defended on the basis that publishing donor details could put them at risk. The exemption is due to end this year but could be extended again by the Northern Ireland Office.
Relationships between developers and politicians are now in the spotlight as a result of the Iris Robinson revelations.
Shortly before he died in 2008 Mr Fraser provided a £25,000 gift via Mrs Robinson to her 19-year-old lover Kirk McCambley for his new business, the Lough Keeper's Inn. Another developer, Ken Campbell, supplied an interest free £25,000 loan.
Mr Campbell this week confirmed being a DUP donor in the past, involving a single contribution of £4,000-£5,000.
The Electoral Commission, which regulates political donations in the UK, is not becoming involving in the Iris Robinson case. It has adopted this stance on the grounds that the money provided by the two developers to Mr McCambley was not in connection with political activity.
A spokesman said: “The Electoral Commission regulates donations to political parties and regulated donees that are in connection with their political activity — otherwise known as ‘controlled donations'.
“After considering this matter, we have concluded on the basis of the information available to us that no controlled donations to Mrs Robinson took place.
“We therefore will not be moving to a review. However if any further information came to light, we would, or course, consider this.”