THE DUP transferred £9,000 from the donation it received for its Brexit campaign into normal party funds.
Details of the funding emerged as the DUP last night continued to face questions over a pro-union group bankrolling its £425,000 Brexit campaign.
Amid mounting pressure to make public the mystery donor, the party yesterday confirmed it was financed by the Constitutional Research Council (CRC).
More than half was spent on a £282,000 front-page wraparound advertisement in the British newspaper Metro – a publication not circulated in Northern Ireland.
More than £10,000 was spent in Northern Ireland through design work and adverts in local newspapers.
CRC is a group of pro-union business figures chaired by Richard Cook, a former vice chairman of the Scottish Conservative Party.
DUP MP Jeffrey Donaldson said CRC approached the party "to support our campaign during the referendum because it supports unionist causes in the United Kingdom".
But the Lagan Valley MP also revealed some of the funds were not used in the EU referendum.
"We received I think £435,000 from the CRC. Of that we spent over £425,000 in the EU referendum campaign," he said.
"We had about £9,000 left which with their agreement we transferred to our normal funds for pro-union campaigning.
"We are giving total transparency on this."
The names of donors in Northern Ireland are automatically withheld due to Troubles-era rules which sought to protect their security.
That had prompted speculation that prominent Leave campaigners were using the DUP to support the Leave campaign without the need to publish their names.
But Mr Donaldson rejected that suggestion, saying that CRC donated to the DUP because the main Leave campaign had already reached its spending limit.
He outlined the details hours before the Electoral Commission published information of campaign spending on the EU referendum.
The figures revealed that more than £32m was spent overall spend by parties in the UK during the Brexit campaign - with the Remain campaign spend coming in at £15.1m compared to £16.4m funded by donations for Vote Leave.
Mr Donaldson told the BBC that his party "wanted to be involved in the referendum at a national level".
"This referendum wasn't going to be won or lost in Northern Ireland, it was going to be won or lost on a national basis," he said.
Campaigning website Open Democracy, which last week highlighted the lack of transparency, raised further questions about the donation.
It said the DUP confirming the donor "tells us nothing about the true origins of their vast campaign donation", adding: "They merely opened one curtain to reveal another behind it."
Alliance leader Naomi Long claimed the DUP only released the information because of public pressure.
"Would the DUP have campaigned as vigorously for Brexit had they not received a large donation to do so? How does that set against the previous allegations by Arron Banks that they were essentially charging a fee to join a Leave campaign? All of those questions need to be answered and answered openly," she said.
Mr Banks, a multi-millionaire who poured millions of pounds into the campaign for the UK to leave the EU, previously claimed that the DUP demanded money to back him.
The DUP denied the allegations made by Mr Banks in a book called The Bad Boys Of Brexit.
Ms Long added: "We now need to see the full list of donors to all political parties in Northern Ireland, not just the DUP."
Sinn Féin's Conor Murphy said the DUP spending most of its funding in Britain where the party doesn't stand for election "raises serious questions about transparency".
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:: What is the Constitutional Research Council?
THE Constitutional Research Council (CRC) may have bankrolled the DUP's Brexit campaign, but very little is known about the organisation.
It has been described as a group of pro-union businesspeople based in Britain, but its size and membership make-up remains unknown.
The group's chair is Richard Cook, a former vice chairman of the Scottish Conservative Party.
Mr Cook (45) was formerly chief executive of Cook Consulting (UK) Ltd, which was dissolved in June 2015.
In 2012 the firm signed agreements to deliver environmental projects in Karachi worth nearly $1bn (£640m).
There are few references to CRC's activities online, but it's not the first time the group has made political donations.
According to the British parliament register of interests, it made a £6,500 donation to Conservative MP Steve Baker to fund hospitality for European Research Group members.
And last year it funded a poll by Survation on the popularity of Tory leadership contenders, with Theresa May emerging as the favourite among those surveyed.
In yesterday's Glasgow-based newspaper The Herald, Mr Cook said CRC would donate to a pro-union campaign if a second Scottish independence referendum is called.
