Prime Minister Gordon Brown and his allies stand accused of distorting the facts as the parlimentary vote on 42 days detention for terror suspects looms - with church figures joining the critics.
The Church of England's Mission and Public Affairs Unit has emailed information to 646 MPs in the run up to the vote, urging them to vote to preserve civil liberties.
The Rev Dr Malcolm Brown, the C of E's mission and public affairs director, told journalists that "any extension [of the current 28 days] will unacceptably disturb the balance between individual liberty and security needs."
Last night, the director of the well-regarded civil rights group Liberty, Shami Chakrabarti, herself a barrister, accused the government of "sexing up" its dossier of cases which, it alleges, illustrate the need to allow lengthy detention without trial.
The term "sexing up" is one that echoes opponents of the Blair government's case for war in Iraq, subsequently uncovered as faulty and exaggerated.
Ms Chakrabarti said that in some cases Liberty had examined, the evidence sought against terror susupects was actually available within 4 or 12 days.
Senior police chiefs have backed the 42 day plan, but others within the force have deep unease - and the British government has been strongly criticised for its proposal by lawyers and judges, ex-PM John Major, the opposition parties, human rights groups, senior European politicians, religious and secular figures, diplomats and academics.
The Director of Public Prosecutions has also expressed unease over the 'safeguards' the government says it is incorporating.
Jonathan Evans, head of the security service MI5, said the organisation was not best placed to advise because it was not responsible for prosecutions or criminal investigations.
Scotland's Lord Advocate Eilish Angiolini told the BBC she was "not aware of any case [since 2000] where an extension of the period beyond 28 days would have been required".
Critics say that Gordon Brown, under massive pressure domestically, is using the vote as a "political virility symbol", applying huge pressure on rebel Labour MPs and offering concessions on bills and government attention to pet projects in exchange for votes.
As it is, he may have to rely on Democratic Unionist Party botes from Northern Ireland to win. Civil libertarians have vowed to campaign on.
Simon Barrow, co-director of the religion and society think tank Ekklesia said today: "The case against lengthy detention without trial, on both civil rights and security grounds, is very strong indeed. The way to combat violent extremism is not through clamping down on basic legal and human rights."
He added: "The government will bring shame on itself if it 'wins' this vote. People of all faith and none are united in wanting to see fairness as the founadtion of a just and free society. The 42 day plan compromises that badly."
The parliamentary vote will take place at about 1800 BST. Frantic lobbying on all sides is likely to continue throughout the day.
MPs have been briefed on the position taken by the Church of England in advance of the debate in the House of Commons today.
The Church says the various “concessions” or adjustments to the proposal offered by the government in recent weeks have not addressed the central concerns expressed by the General Synod when it debated the subject, in February 2008.
The C of E's ruling body said: “We believe that a convincing case for the extension of the maximum period of detention without charge beyond 28 days has not been made out. This central point has not been addressed in the various 'concessions' or adjustments to the proposal offered by the Government in recent weeks. We believe that any extension beyond 28 days will unacceptably disturb the balance between the liberty of the individual and the needs of national security.”