The money from the Constitutional Research Council was spent on pro-Brexit advertising throughout the UK. The group is chaired by Richard Cook, a former vice chairman of the Scottish Conservative and Unionist Party, however, little other information appears to exist on it.
Mrs Long said the DUP should now follow through and release the names of other donors to the party, which Alliance already does voluntarily.
“While it is welcome the DUP were forced to make the move of revealing the donor in this instance, the information released brings little clarity to the situation, as the usual checks fail to reveal much information about the Constitutional Research Council.
“The Brexit campaign sold voters a lie about the influence of faceless EU bureaucrats but now it appears faceless donors were pulling the strings of the campaign.
“Any pretence security concerns were the only reason the DUP did not follow through on previous pre-election commitments in 2014 and 2016 to move to full transparency are exposed as the smokescreen they are, given the chair of this group was Scottish.
“I therefore call on the DUP and every other party to do what Alliance already does and voluntarily reveal the names of the rest of their large donors now so the public can judge for themselves whether or not they are being influenced by those with deep pockets or are acting in the public interest.”