A Scots Conservative at the centre of the row over a £435,000 Brexit donation has accused a Westminster committee of “grandstanding” and making “defamatory” comments about him.

Richard Cook, chair of the shadowy Constitutional Research Council (CRC), accused the Tory committee chair of laziness after he was quizzed about the donation.

Official correspondence also reveals Cook twice declined to answer questions about the source of the funds.

The little-known CRC gave the Northern Ireland-based Democratic Unionist Party, which is pro-Brexit, £435,000 during the EU referendum campaign.

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However, the bulk of the money was spent on an advert in the Metro newspaper, which is not distributed in Ulster.

The sum did not have to be publicly declared - at that time, donations to parties in Northern Ireland could remain secret - but the DUP voluntarily confirmed the details.

The spotlight has since fallen on where the CRC, set up in 2014 to campaign for Scotland to remain in the Union, got the so-called “dark money”.

As an unincorporated association, the CRC does not have to publish accounts, reveal donor identities or say who is member of the organisation.

One of the few facts to come out about the body is that it is chaired by Cook, a former vice-chair of the Scottish Tories and an erstwhile party candidate.

Speaking to the Herald in 2017, Clarkston-based Cook said the CRC is regulated by the Electoral Commission, operates solely in the UK and only accepts donations from eligible UK donors.

He declined to offer any information on the identities of Council donors or members, but said Scots had made financial contributions.

The source of the funds has become a national story and a matter of interest for Westminster’s Digital, Culture, Media and Sport Committee (DCMS), which is investigating disinformation and ‘fake news’.

This newspaper reported in November that the DCMS had contacted Cook about the donation, but the Committee said they had received no response. Cook’s spokesman denied this claim.

Letters published on the DCMS website reveal the escalating tensions between the Committee and the businessman.

On November 2nd, Committee chair Damian Collins, a Tory MP, wrote to Cook:

“As part of the inquiry, we would like to ask about the £435,000 donation made to the DUP’s Leave campaign during the lead-up to the EU referendum. The DUP has reportedly disclosed that the money was funnelled via the Constitutional Research Council. We would like to know the source of the funds, and how it was presumed that the money would be spent.”

Collins added that the DCMS, depending on Cook’s answer, would also decide “whether to request that you appear in person before the Committee”.

An angry Cook responded three days later: “The only ‘fake news and disinformation’ here is that which is contained in your letter...Had you taken the time to research the clear statements and information already published in relation to this matter you would be in no doubt as to the permissibility of the Constitutional Research Council’s donation.

He continued: “Plainly a permissibly [sic] donation by a permissible donor in no way falls under the remit of your inquiry, save that the stories made up about it by conspiracy theorists and various parliamentarians who are too lazy to check for facts - which may now include you - are examples of disinformation.

“It is very hard to see what value there is in me appearing in front of a committee whose chair, and at least one other committee member, have literally spread disinformation about me. I must separately note that your insinuation that I ‘funnelled’ anything is defamatory.”

Days later, Collins again wrote to Cook to claim he had received no reply and said the Parliament “may” need to look at its formal powers, such as summoning witnesses.

In response, Cook wrote that he had responded to the first letter and said the Committee had received “categoric” evidence from the Electoral Commission which showed that the donation was permissible and legal.

He concluded: “True to form you are not letting reality get in the way of grandstanding. Your actions are the source of the ‘fake news’ you claim you wish to investigate.”

SNP MP Brendan O’Hara said:

“Both the tone and the content of Richard Cook's response to the Select Committee are extremely disappointing, and I believe falls far beneath what the Committee would have expected from a former vice chair of the Scottish Conservative party.

“His claim that the Conservative chairman, and other members of the Committee, have spread false information about him is patently absurd and can be seen for what it is - a ridiculous attempt at dodging serious questions of the activities of his secretive organisation.

“The DCMS Committee has acted in good faith throughout this Inquiry and that includes in our attempts to get to the bottom of the massive donation made by the Constitutional Research Council to the DUP. For Mr Cook to suggest otherwise is a complete nonsense."