David Davis is set to kick off his civil liberties campaign for real by officially quitting as an MP.
The former shadow home secretary will challenge Gordon Brown to put up a candidate to fight him in the Haltemprice and Howden by-election as he hands in his letter of resignation to the Treasury.
Mr Davis sparked anger and bewilderment among his Tory colleagues last week by announcing his unconventional protest, insisting he wants to make a "noble" stand after Government Whips used "shabby" tactics to force through 42-day pre-charge detention of terror suspects.
But Tory leader David Cameron was not informed until the eleventh hour, and ministers gleefully seized on the move as evidence of division and indiscipline.
Some Conservative MPs suggested the 59-year-old was on an "ego trip" or had "gone mad" - although polls have suggested strong support among voters for his stand.
The Lib Dems are backing Mr Davis's "principled" protest, while Labour has refused to say whether it intends to field a candidate until he formally resigns.
But the Prime Minister came close to confirming that the party will "opt out" of a confrontation last week by branding the protest "a stunt" and "a farce".
Mr Brown delivered a speech on civil liberties in which he tackled many of the issues raised by Mr Davis - including 42-day detention, the burgeoning police DNA database, and ID cards. However, he carefully avoided mentioning the former frontbencher by name.
Mr Davis will apply for the archaic post of Steward and Bailiff of the Chiltern Hundreds in order to resign, because Parliamentary rules prevent MPs from quitting outright. The last holder of the job was ex-Prime Minister Tony Blair.
Mr Davis will be defending a 5,116 majority in the Haltemprice and Howden by-election, which is likely to take place on July 10.
