Michael Gove has refused to rule out being the source of claims that the Queen backed an exit from the European Union during a private meeting.
During a Brexit campaign visit in Hampshire, the Justice Secretary said: "I don't know how the Sun got all of its information."
When pressed by reporters, Mr Gove added: "I've already said that enough has been said about this story so I don't think it's appropriate to say any more than I've already said and others have already said."
Mr Gove is one of several cabinet ministers campaigning for Britain to leave the European Union.
Labour MP Wes Streeting told ITV News that Mr Gove “seems to have issued a non-denial denial”.
“I think he needs to just say one way or another if he did it, and if he did I think he needs to apologise," he added.
Buckingham Palace has lodged a formal complaint with the Independent Press Standards Organisation (Ipso) about the report which appeared under the headline: Queen Backs Brexit.
The Palace also confirmed Her Majesty remains "politically neutral" over the referendum outcome and added: "We would never comment on spurious, anonymously sourced claims."
Mr Gove said the Ipso investigation into the leak was a "matter for them" and refused to say if he would cooperate with it.