IAN Blackford has called for an investigation into the “shady business” behind claims of illegal co-ordination between different groups involved in the 2016 pro-Brexit campaign.

The intervention from the SNP’s Westminster leader comes after the whistleblower behind allegations about the misuse of Facebook users’ data told MPs he was “absolutely convinced” that different pro-Leave groups had worked to a “common plan” allowing them to get around strict spending limits.

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At Prime Minister’s Questions yesterday, Blackford said “all allegations of improper spending during the EU referendum must be fully investigated”.

He will write to Theresa May asking her to support a probe by the Electoral Commission, and calling on her to issue details of transactions between certain pro-Brexit groups.

Former Cambridge Analytica employee Chris Wylie and other whistleblowers have claimed the official Vote Leave directed other campaign groups in order to avoid a £7 million legal limit on election spending, in breach of electoral law – something the official Leave campaign and its leaders deny.

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The donations Blackford wants probed include one for £425,000 from the Constitutional Research Council (CRC) to Northern Ireland’s DUP. The CRC is chaired by Richard Cook, a former vice-chairman of the Scottish Conservatives.

In the Commons, the SNP MP asked: “The public must have trust in our political process. Does the Prime Minister agree with me that transparency in political campaign spending and the integrity of electoral laws across the UK must be upheld? Will the Prime Minister join with me in saying that all allegations of improper spending during the EU referendum must be fully investigated?”

May responded: “We have laws about election spending that parties are required to abide by.

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“I understand that any allegations that have come forward in respect of spending during the referendum have already been investigated by the Electoral Commission, but of course it’s right that allegations are investigated by the Electoral Commission.”

Blackford added: “We know that before the EU referendum the DUP received £425,000 from the Conservative-run Constitutional Research Council ... we know some of the money was given to AggregateIQ, a reported franchise of Cambridge Analytica.

“We know that Chris Wylie is absolutely convinced of a common purpose between Vote Leave, BeLeave, Veterans for Britain and the DUP.

“The shady business of data mining and undermining electoral law goes right to the heart of the Prime Minister’s party.

“Will the Prime Minister issue the full details of the transactions between the DUP and the Scottish Tory-linked CRC?”

May replied: “I understand that this is a matter that has already been investigated twice by the Electoral Commission and he raises questions about inquiries. If there are allegations of criminal activity that should be taken to the police. The regulator of election spending is the Electoral Commission so if there’s an allegation of breaches of campaign spending, or campaign funding rules, then this should be taken by the Electoral Commission.

“My understanding is the Electoral Commission does indeed investigate these and will continue to do so when allegations are brought to its attention.”

Last year it emerged the CRC, a pro-Union group comprising a string of business figures, provided the resources for the DUP to pay for a full wrap-around advert in the free Metro newspaper in the days before the vote, even though the paper is not published in Northern Ireland.

The money also went to other campaign material distributed across the country.

Last year it emerged the CRC, which was established amid disquiet about the way Better Together ran the pro-Union campaign in the 2014 referendum, intends to bankroll unionist groups in any new independence referendum.

It was reported at the time the CRC backed Brexit in the EU referendum after coming to the conclusion that leaving the EU would be good for the Union and “bad for nationalism”.

Because of the Troubles, donations to political parties in Northern Ireland are confidential amid fears of reprisals if donors are identified.