The justice secretary has blocked the release of minutes of a 1997 cabinet committee meeting on devolution.
Jack Straw said he believed disclosure would put the convention of collective cabinet responsibility for decisions "at serious risk of harm".
The UK's information commissioner said he would "carefully consider" Mr Straw's reasons for using his veto.
The only other time he has used it was to block the release of cabinet minutes relating to the Iraq War.
The minutes covered the meetings of a committee which was set up to "promote legislation relating to the devolution of power to Scotland, Wales and the English regions chaired by Lord Irvine of Lairg"
Cabinet minutes relating to military issues, you can make an argument for censoring on the grounds of national security and not merely to protect the "concept of collective cabinet responsibility". But that argument falls apart when applied to devolution issues.
Is Straw, in truth, actually attempting to censor records of division on the subject that existed within the Labour higher echelons at the time?