David Davis's decision to quit Parliament in protest over MPs' decision to back the extension of pre-charge detention to 42 days caught Westminster completely by surprise on Thursday.
The shadow home secretary's announcement immediately sparked speculation that he had fallen out with David Cameron with whom he fought a sometimes acrimonious battle for the Tory Party leadership in 2005.
Cameron was quick to say Davis made a "courageous" choice - though he sounded less than warm when he stressed it was a "personal decision" and nothing to do with him, shadow cabinet or the wider Tory Party. He also announced he was appointing Dominic Grieve as the new shadow home secretary in a swift turnaround of frontbench personnel.
The Lib Dems will not field a candidate in the by-election in Haltemprice and Howden after Davis contacted that party's leader Nick Clegg late on Wednesday night. Clegg said the "unnecessary and illiberal" 42 day proposal transcended party politics.
Standing outside the Palace of Westminster, because the Speaker told him he could not deliver his statement in the Commons chamber, Davis said he was resigning over the "insidious and surrepitious erosion" of British traditions.
He cited not just the 42 days - which he speculated could be extended still further - but ID cards, the assault on jury trials, "shortcuts with our justice system" as a wider attack on some of the rights dating back to the Magna Carta.
"It is incumbent on me to take a stand to oppose the strangulation of British freedoms," he told reporters before stressing he would not be campaigning on other national issues.
There is no point in re-running the Crewe and Nantwich by-election, he said.
Davis's decision isn't without precedent in the annals of British political history. In 1910 George Lansbury became Independent Labour Party MP for Bow and Bromley, but after two years clashed with Liberal prime minister Herbert Asquith in the House of Commons over the issue of women's suffrage.
Like Davis, he too quit his his seat in order to run in a by-election in support of the Suffragette cause. He lost and didn't return to the Commons for a decade.
On the other hand, in 1972 Dick Taverne quit as Lincoln's MP and ran as an independent in the by-election because he disliked the leftwards drift of the Labour Party. He won but was booted out by Margaret Beckett (then Jackson) at the following general election.
More coverage: Hazel Blears asks what's really going on in the Tory Party. Martin Bright praises David Davis's decision plus don't miss Amnesty International's Sara MacNeice for her reaction to the 42 days decision