Anger over continued delays in the publication of the report into the Iraq war has swung back against the government with allegations that “vested interests” have tried to suppress evidence.

The inquiry, chaired by former Whitehall mandarin Sir John Chilcot and established in 2009, has yet to name a date for the publication of its report, which is expected to heavily criticise a number of politicians, including former prime minister Tony Blair, and several intelligence and defence officials.

The delay has dismayed the families of armed forces personnel killed in the conflict and led to complaints that it is prolonging their anguish. It has also seen Chilcot come under criticism from MPs, with David Cameron and other ministers repeatedly expressing their frustration.

But last night John Baron, Tory MP for Billericay and a member of the Commons foreign affairs committee (FAC), said that he was in “no doubt” that forces within the establishment had held up the inquiry by failing to meet its obligation to disclose key documents. Chilcot has revealed that new evidence came to light only when witnesses to the inquiry made reference to them in their responses to the “Maxwellisation” process, under which people facing criticism are given a pre-emptive right of reply.

In a statement last week, Chilcot made pointed reference to the government’s obligation to provide “all relevant documents” to the inquiry. But he described how the Maxwellisation process had “led to … the identification of government documents which had not been submitted to the inquiry and which have in some cases opened up new issues”.

Chilcot has already indicated that he considers some of the new evidence significant enough to be published with his findings, which has extended the already lengthy process for requesting the declassification of relevant documents from the government.

Baron told the Observer: “I have no doubt that some vested interests have resisted disclosure and this has helped delay progress. Having been interviewed by Sir John as part of the inquiry, I believe he is determined to address the central issue as to whether No 10 intentionally misled the nation as to the case for war.”

Although Baron did not specify which figures he had in mind, the role of cabinet secretary Sir Jeremy Heywood has previously come under scrutiny. Heywood was principal private secretary to Blair in the runup to the war and is ultimately responsible for deciding which documents the inquiry can cite and publish in support of its findings. The Cabinet Office declined to explain why government departments did not give the new documents to the inquiry in the first place or why “Maxwellees” were able to cite them. Neither is it clear whether the inquiry has now received all the documents it has requested.

When pressed on these questions, a government spokesman said: “We have co-operated fully with the inquiry, including providing it with all relevant documents.” He added: “The civil service continues to make every effort to ensure the inquiry has all it needs to complete its work as soon as possible.”

A spokeswoman for the inquiry also declined to be drawn on the matter.

Baron joins FAC chair, Crispin Blunt, in expressing support for Chilcot. Last week Blunt told the BBC that insisting on a deadline for its report could “wreck the inquiry”.

There have been calls, notably from the Lib Dem leader, Tim Farron, for hundreds of documents submitted to the inquiry that have already been declassified to be released for publication now.

Although there is no legal block on the release of these documents, the government has refused a freedom of information request for their disclosure, on the grounds they will eventually be released alongside the inquiry’s final report.