Beleaguered UK Transport minister Mr Stephen Byers has told the House of Commons a "very small number of civil servants" have attempted to undermine his department.
He says both Ms Jo Moore and Mr Martin Sixsmith had agreed to resign in the wake of the Whitehall email row.
Mr Byers said his view was that Mr Sixsmith should not be given a job anywhere else in the British government.
He added that he was not in a position to enforce that view.
Shadow transport secretary Ms Theresa May charged: "Today is a day of humiliation for the Secretary of State." She again demanded his resignation.
Mr Byers said if his answers on ITV1's Dimbleby programme had implied he had not put forward a view or made it known to others "that's obviously something I regret".
The minister said, in an emergency Commons statement, that in the wake of the Ms Jo Moore email row: "What we had was a concerted attempt by a very small number of civil servants in the press office to undermine the department."
He said that the few civil servants believed to be involved were being investigated and stressed: "The vast majority work in a very good, committed, and dedicated manner."
Mr Byers said there had been a number of meetings and discussions involving Mr Sixsmith, in an attempt to resolve the terms of his departure. The Transport Secretary added: "I have not been directly involved in those arrangements."
Mr Byers said: "We were clear that the department could not carry on with the communications department in the state it was. I believed that both should go. Jo Moore agreed to resign. Martin Sixsmith agreed to resign. I announced the resignations."
The Transport Secretary said he had not met or spoken to Mr Sixsmith since his resignation. He added: "I made it clear to Sir Richard Mottram, however, that in my view ... Martin Sixsmith should not be given a job elsewhere in the Government."