THE "shady business" of data mining and undermining electoral law "goes right to the heart" of the Prime Minister's party, the SNP Westminster leader has claimed.

Ian Blackford raised the issue of EU referendum campaign spending during Prime Minister's Questions arguing that all allegations of improper spending must be fully investigated.

Theresa May said it was "right" that allegations were investigated by the Electoral Commission adding that "if there are allegations of criminal activity that should be taken to the police".

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Mr Blackford, the MP for Ross, Skye and Lochaber 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?"

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

"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."

Mr Blackford called on Mrs May to issue details of transactions between certain pro-Brexit groups.

He said: "We know that before the EU referendum the DUP received £425,000 from the Conservative-run Constitutional Research Council (CRC)...we know some of the money was given to AggregateIQ (AIQ) a reported franchise of Cambridge Analytica (CA).

"We know that (whistle-blower) 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?"

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Mrs 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."