Sinn Féin's Paul Maskey has called on the DUP to reveal exactly who was behind its £435,000 Brexit donation

SINN Féin is to meet the Electoral Commission today to discuss the £435,000 Brexit donation made to the DUP by a pro-union group.

The meeting comes after fresh details emerged of the party's spending during the EU referendum campaign.

Paul Maskey, who will lead the Sinn Féin delegation, said there are "serious public concerns" about the money the DUP received from the Constitutional Research Council (CRC), an organisation headed by former Scottish Conservative parliamentary candidate Richard Cook.

Mr Cook has previous business associations with a former head of the Saudi Arabian intelligence service.

The exact source of the money given to the DUP is not known, but the party insists it has fully complied with Electoral Commission regulations around party donations.

Alistair Carmichael, a former Northern Ireland spokesman for the Liberal Democrats, told The Irish News earlier this week that the episode had highlighted potential flaws in legislation governing political donations.

Speaking ahead of today's meeting with the commission, Mr Maskey called on the DUP to reveal more information about the donation, which among other things paid for a wrap-around ad in the Metro newspaper, which is not circulated in Northern Ireland.

"The DUP have yet to reveal where this money, paid by the mysterious Constitutional Research Council, actually came from," he said.

Meanwhile, receipts uncovered by investigative website The Detail show that the DUP paid a company in England for pro-Brexit merchandising ahead of the last June's EU referendum.

The party paid almost £100,000 to the English branding company for what appeared to be 100,000 window stickers, 50,000 badges, 15,000 plastic boards, 5,000 bags and 7,000 t-shirts.

A separate receipt showing a DUP transaction with a company in Northern Ireland prior to the referendum showed the party spent just under £1,000 on 38,000 Brexit flyers.

An additional £1,600 was paid to a second Northern Ireland firm involved in mail and marketing services.

The DUP last night repeated its assertion that it had gone "beyond all requirements" in relation to rules surrounding the EU referendum campaign.

It also said the Electoral Commission had raised no issues about donations.

"Everything written about this issue over recent days has been old news conveniently reheated during an election campaign," a spokesman said.

He added that "we await similar questioning of other parties about their donations" including Sinn Féin.