The Minister for Justice has insisted the two parties of Government are at one on what needs to be done to agree a "comprehensive deal" on Northern Ireland.
Mr McDowell said he predicted there would be "no deal" provided the IRA was given room to manoeuvre on the question of ending criminal activity.
He said both parties and both sets of ministers were "operating from the same hymn sheet" on the question of IRA criminality and the conditions for the release of the killers of Det. Garda Jerry McCabe.
Speaking on RTE's Today With Pat Kenny, Mr McDowell said the agreement towards which the Irish and British governments are working was "saveable, doable and would be a brilliant step forward for the people of Ireland north and south" if it was put in place.
Mr McDowell also insisted there was no "wriggle room" for the IRA on the question of the cessation of criminal activity.
The Minister for Justice, Mr McDowell
The Minister claimed the Dublin brigade of the IRA had been, until recently, engaging in "constant criminality" to fund the Provisional movement.
On the question of the proposed release of the McCabe killers, Mr McDowell said the men were not the subject of any right or expectation of early release under the Belfast Agreement and that they had not even been convicted at the time of that deal.
"And that has always been the Government's clear position. We said it publicly at the time, ever since, in the courts and, despite what you hear from some people, the Supreme Court has upheld our position that they are not entitled to early release."
He said there was not "a shred of truth" in Mr Gerry Adams's contention that the High Court and Supreme Court had in fact upheld the right of the men to be released under the terms of the agreement.
The Minister also said the Taoiseach had never shaken hands with Mr Adams and Mr Pat Doherty of Sinn Féin on the issue of the release of the men.
He said he did not want to go into all the details of the proposed release of the killers, but indicated their release would be conditional upon the IRA ceasing all criminal activity.
Mr McDowell added: "It is my understanding and certainly it would be part of any comprehensive settlement that the IRA would put all of its arms beyond use and that General De Chastelain would oversee that process and the issues, as we know, are in relation to verification of that process."
The Minister for Justice, Mr McDowell
Mr McDowell said criminal activity, such as the botched robbery which resulted in the death of Garda McCabe, could not be consistent with an IRA ceasefire.
He said the IRA and Sinn Fein were "not separate organisations".
The end point of the entire process was whether Sinn Féin members could sit around the Cabinet table in the republic or around the executive table in Stormont and that this "must be contingent on whether or not their party accepts that there can be no question of any further violence," he said.
Mr McDowell said: "It means that if Gerry Adams is to be taken seriously as an ordinary politician that he must sever all connections with an organisation which engages in these activities. If that organisation is not willing to say it's giving up these activities then Gerry Adams cannot sit around a cabinet table and participate in the executive activities of Northern Ireland."
Mr McDowell said: "I'm predicting that there's no deal as long as they have room to manoeuvre on those grounds and I'm not going to accept any more of this guff from people saying that knee-cappings and torture and all of these things have nothing to do with Sinn Féin. Absolutely not. And it's a red-line issue for the Government."
He added that Mr Adams had been doing an "old trick" of trying to divide the PDs and Fianna Fáil. But the Taoiseach had said the two governments were "absolutely at one" on the "red-line" issue. Any ambiguity on the issue would be "entirely destructive".
If Sinn Féin members go into government north or south of the border at some future time, it was on the basis that the organisation to which they are allied and "to which senior members pay allegiance" could not be involved in criminal activity.