John Prescott has resigned from the Privy Council in protest at a delay to new press regulation plans that "borders on a conspiracy".
The Labour former cabinet minister took the rare step of withdrawing from the prestigious body over what he said was a "political" hold-up.
It could even "embroil the monarchy in a possible conflict with Parliament and political division between the parties", he suggested.
A cross-party Royal Charter setting up a new system of self-regulation along the lines recommended by last year's Leveson Inquiry into phone-hacking had been expected to be approved by a committee of the Council.
But this week's meeting – led by Deputy Prime Minister Nick Clegg – will instead consider a rival version drawn up by the industry and backed by most newspapers.
Victims of press intrusion have reacted furiously to the delay – which means the Commons-backed system will not be considered until the autumn.
Prime Minister David Cameron told MPs though that the Government had to follow the "correct legal processes" – which means priority must be given to the first of the Royal Charters to be formally submitted for consideration.
He insisted that he remained committed to the cross-party proposals and said there were "serious shortcomings" in the industry version.
Lord Prescott – a member of the Privy Council since becoming Labour's deputy leader in 1994 – used his column in the Sunday Mirror to suggest the Government had deliberately "dragged its feet".
The peer – who will no longer be entitled to be referred to as "the right honourable" as a result of quitting – said he had only "reluctantly accepted" the cross-party "compromise" on the original Leveson recommendations.
"But this Wednesday the Privy Council won't be considering Parliament's Royal Charter. It will be the rival Press Board of Finance (PressBof) Charter, written by press owners but not supported by all newspapers.
"The Government dragged its feet in further consultation and the Press industry put in its divided charter first. The rules and procedure, we are told, now mean it has to be considered first and consulted upon before Parliament's version, which is clearly a political decision by the Government.
"However the PressBof Charter deals with regulation of an area of conduct already the subject of settled government and legislative policy. This Charter is in fact a challenge to establish government policy in which ministers attending the Privy Council cannot have an open mind.
"The process of examination and implementation of Parliament's version could last until January 2015. If it failed, then it would be referred back to Parliament, four months before the next General Election.
"I believe this approach borders on a conspiracy to delay Press regulation. Much worse, it will embroil the monarchy in a possible conflict with Parliament and political division between the parties."
Prescott said he had never wanted to join the Privy Council but was persuaded he must do to have access to certain state documents.
Revealing his resignation, he pointed out that the only time all members of the Council met – presently numbering some 550 serving and former cabinet ministers, party leaders, Archbishops, senior judges and other high office holders – was at the change of a monarch.
"Except I won't be there. I have resigned as a Privy Councillor on this point of principle about how the charters are considered," he wrote.
"I sent off my resignation letter on Friday. The Privy Council must put Parliament and Parliament's Charter first."
Resignations from the Privy Council are rare – and usually prompted by personal disgrace.
Chris Huhne became just the fifth to do so earlier this year when he quit the Cabinet and Parliament after admitting perverting the course of justice by dodging speeding points.
The press-backed Royal Charter is backed by a majority of newspapers and would avoid any state underpinning for the new regulatory regime.
It is understood that Culture Secretary Maria Miller's Department for Culture, Media and Sport does not want to leave itself open to legal challenge by failing to follow the process to the letter.
The industry charter is on the agenda to be noted at the July 10 meeting of the Privy Council, but no substantive discussion or decision is expected at that point. Because the Privy Council does not meet over the summer, the earliest date on which a decision could be made is in the autumn.
Campaign group Hacked Off – which was involved in the late-night negotiations with political leaders that produced the cross-party Charter – applauded Lord Prescott's decision.
"He is expressing the frustration felt by very many people, including victims of press abuses, at the stalling of much-needed change on grounds related to the supposed procedures of this obscure body," a spokesman said.
"Victims only accepted the use of the opaque, medieval Royal Charter process very reluctantly, as it was clearly second best to a straightforward piece of legislation.
"It now appears that their fears were well-founded.
"The decision to put the press barons' charter through ahead of the parliamentary one is, as Lord Prescott says, a political move by sections of the Government who want to buy time for their friends in the press.
"The policy of all parties in both Houses of Parliament is clear and settled. If a small group of newspaper editors and proprietors, who are not even representative of the industry as a whole, are able to drag the cross-party agreement into a ditch at this stage, it will be an affront to democracy.
"It is unprecedented in modern times for a Privy Councillor to resign as an act of protest. We hope that the Government now recognises the strength of feeling and takes steps to act urgently, before the hacking trials start in September."