The review is being brought by CAAT against the Serious Fraud Office and is related to the dropped investigation into an arms contract between BAE and Saudi Arabia.
CAAT then took BAE to court in January to force the disclosure of how BAE received the email detailing the group's legal advice.
Mr Mercer said in his affidavit that he did not know who had sent him the package and passed on the email to BAE's head of security Michael McGinty.
According to the court documents, Mr Mercer said that Mr McGinty told him he should not send any more unsolicited material and told him two months later that he had been named as the source of the email.
CAAT told the Daily Telegraph: "We believe the actions of Mr Mercer and BAE raise issues of the utmost public importance."
BAE said it was preparing a statement on the matter.
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