Mr Ross, who appeared before the Iraq Inquiry earlier this month, alleged that "deep state" elements were preventing the inquiry from finding out the true reason for the invasion of Iraq in 2003.
Mr Ross also claimed that the Iraq Inquiry panel, chaired by Sir John Chilcot, was "neither equipped, nor apparently inclined" to challenge witnesses "on the contradictions of their testimonies".
However, he said this "may not be the panel's fault", because he alleged members did not know of the existence of key documents.
Mr Ross claimed: "In these circumstances, it is very worrying that the government machine is still trying to withhold key documents and silence those of us with detailed knowledge of the policy history - and documents."