Current Conservative proposals for a Royal Charter that would oversee a new press watchdog "do not implement the Leveson report", Labour said today.
The Tories yesterday outlined their plans for creating a body to verify a new regulator set up by the industry as the main parties attempt to reach an agreement on press regulation.
Deputy Labour leader Harriet Harman told the House of Commons Labour had been engaging in talks in "good faith", but added: "What Leveson proposes is fair and is reasonable, it protects free speech and protects people from abuse and harassment by the press.
"There can be no justification for watering it down.
"The most straightforward way of implementing Leveson is by statute rather than by Royal Charter and statute, but whatever the route that is chosen it must be the full Leveson not Leveson lite."
Her comments came as Culture Secretary Maria Miller insisted the Tory proposals offered "tough oversight" and ensured a new regulatory body was efficient and effective.
She said: "This is a tough regulation, a tough package and delivers the principles of Leveson."
The Royal Charter she maintained "reflects a principled way forward, proposed by the Conservatives from this side of the coalition and we're clear that it is a workable solution".
But she added "it is only a draft and we will continue to debate it as part of the cross party talks and we will continue to seek to secure agreement".
"We are all committed to the Leveson principles this is about taking the Leveson Report forward and making sure that it will work in practice and the challenge before all of us is to find an agreement, I think the victims deserve nothing less.
Answering an urgent question from Labour on the issue, Miller said the draft Royal Charter published was outside of the normal arrangements for collective agreement and "does not reflect an agreed position" between the Conservative and Liberal Democrat parties.
The Prime Minister, she said, wholeheartedly supported a tough new system of independent self-regulation as outlined by Lord Justice Leveson.
She said: "We continue to have grave reservations around statutory underpinning and as such we have concerns about implementing a press Bill.
"The Royal Charter that I've published will put in place Leveson's recommendations without the need for statutory underpinning, it would see the toughest press regulation this country has ever seen without compromising press freedom."
The Royal Charter, she argued, would implement the principles of Leveson in a "practical fashion" and was the Conservative's Party's alternative to Lord Justice Leveson's suggested use of Ofcom as a verifying body.
She said: "All parties now agree with us that handing further powers to Ofcom, an already powerful body, would not be appropriate."
The Royal Charter, she said, would not create a regulator but rather establishes a body that would oversee the regulator.
Harman outlined her concerns to the Conservative Party's proposals.
She said that through the Privy Council, ministers would be able to tamper with the Royal Charter at any time and urged clauses in statute providing this could not happen.
She said: "The Royal Charter as currently drafted allows the press to be part of the appointment process to the very body whose job is to guarantee the independence of the system.
"Will she take the press out of the appointments system and will she undertake to come forward with changes to the recognition criteria so that what's in the Royal Charter matches rather than dilutes Leveson?"
The vote in the Lords on the Defamation Bill last week showed, she said, that "there will no acceptance of Leveson being watered down or kicked into the long grass".
She warned: "We will be reasonable on this but we will be robust," and added: "History will judge us as having failed in our duty if we do not implement Leveson and do so now."
Miller said it was not in fact Labour policy to implement Leveson in full either, highlighting cross-party concerns over the judge's recommendations on data protection and the role of Ofcom.
And she said the Royal Charter proposal was drafted such that it could not be easily tampered with.
Miller added: "I was pleased there was not a wholehearted rejection of the Royal Charter approach."
The Culture Secretary said the Government had "wholeheartedly rejected" proposals which would have involved media or political roles in the new body.
She told the Commons: "We know the appointment process for the verification body needs to be independent and for those that have read the details of what we are proposing, they will be able to see that is exactly what we are doing."
Miller said it was vital the implementation of Leveson ensured the plan "worked in practice", insisting "certainty and clarity" were key.
Liberal Democrat John Leech (Manchester Withington) said his party backed a statute to implement Leveson.
He added: "But we do accept a Royal Charter could work - unfortunately the draft Royal Charter currently fails to meet the general requirements set out by Leveson."
Leech urged Mrs Miller to accept that as the draft stands, nothing in law protected the charter from changes in future.
She said: "We will continue to work together through this cross-party process to make sure we can come to a consensus here.
"I understand your desire to make sure any verification body had clarity, has certainty and has longevity.
"That is exactly why we have put on to the face of the charter very clear provisions which state clearly any changes would have to have the full support of three party leaders and a two thirds majority vote in both Houses of Parliament."
Chairman of the Culture, Media and Sport Committee John Whittingdale said there was "considerable public impatience" and urged a swift resolution to talks.
He called for the newspaper industry to reach agreement on the direct self-regulator quickly, and added: "Will your approach allow the new body conforms with all of Lord Justice Leveson's recommendations but also that it will allow it to start its work without waiting for legislation?"
Miller said: "You are right, momentum is important. People want to see change, that is very clearly a message that has gone out to the press and it is certainly Something we underline today."
Sir Gerald Kaufman (Manchester Gorton) said the press were attempting to "abolish the licensing hours for the last chance saloon" and urged a deadline to be set for agreement by the press of its own regulation body.
Miller said: "It is something which does require the press to put together a new regulatory regime. Every indication I have is that is exactly what is happening."
Labour's Tom Watson (West Bromwich East), who has campaigned against phone hacking at News International, said: "The Prime Minister looked the Dowler family in the eye and gave them a solemn pledge he would enact Leveson in full.
"Do they deserve an explanation from him as to why that is not the case in these proposals?"
Miller said: "You will know we are absolutely committed to taking forward the principles of Leveson but even more important than that, we want to make sure the approach we take is fully independent of both the press (and) the Government."
Chris Bryant, the Labour MP for Rhondda, said the Government had not published details of meetings between ministers and newspaper proprietors since last June.
He said the Royal Charter looked like a "shabby deal" between ministers and proprietors.
Miller replied: "You know all of those sorts of meetings get published in the usual way."
Bryant later raised a point or order about the reply, but Mrs Miller declined to comment further when invited to do so by Speaker John Bercow.
Tory MP Zac Goldsmith (Richmond Park) said arbitration processes must be free to access for people wronged by the press.
Miller replied: "You will know from reading Lord Justice Leveson's report he feels it is very important to have a cost effective process and there is ready access.
"We are trying to take that objective, to make it work, to make it work in the way it does in many other areas of the law in terms of tribunal access."