Because of continuing donor secrecy in Northern Ireland, no details of where the £425,000 donation – almost certainly the biggest single political donation in the history of Northern Ireland – came from would not have been made public without the consent of the DUP.
However, in February, under pressure to explain the huge sum, the DUP took the unusual step of voluntarily naming the donor as the Constitutional Research Council (CRC), run by a former Scottish Conservative candidate called Richard Cook.
It quickly became clear that Mr Cook is of modest means and the money – much of which was used to fund expensive wraparound adverts in the Metro newspaper outside Northern Ireland – originated elsewhere.
There is no legal record of the CRC, which is neither a charity nor a company registered at Companies House, and Mr Cook has declined to name any of its other members or funders.
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Days after the DUP revealed Mr Cook’s involvement, the Open Democracy website revealed that he had been in business with a now deceased former head of Saudi intelligence, Prince Nawwaf bin Abdulaziz Al Saud.
This week, responding to questions from Open Democracy, the DUP’s Jeffrey Donaldson said that he had been unaware of that Saudi link.
However, Mr Donaldson firmly said there was nothing improper about the donation and said that the DUP had been keen to play a full role in what was a national referendum.
The Electoral Commission has said that unincorporated associations “can’t act as the agent for an impermissible donation” and that the onus is on the recipient to confirm the donor’s eligibility.
In March, Mr Cook said it was “laughable” to describe the source of the funds as “shadowy” and insisted that all the money came from UK businessmen – but declined to name them.
When asked if it was attempting to establish the original source of the money, the DUP said it had “gone beyond all requirements in relation to our participation in the European Referendum campaign”.
“The Electoral Commission has raised no issues in relation to the DUP campaign, including the donation which came from a permissible donor, who in turn are themselves regulated by the Electoral Commission.
“If there were any issues with the campaign then the commission would launch an investigation and impose any sanctions deemed necessary.”
When the Electoral Commission was asked if it was investigating the situation, a spokesman said: “The commission is legally bound to retain confidentiality about donations to political parties in NI.
“Whether parties or donors choose to make this information available is a matter for them. In that event, the commission remains bound by this legal requirement for confidentiality and would therefore be unable to comment specifically on your query.”
However, he added: “We can confirm that we are not currently conducting any investigations in respect of donations to the DUP.”