The Parliamentary Voting System and Constituencies Bill, that's what. Ostensibly a move to restore the public's faith in parliament, the coalition government have long wanted changes in the way people vote, for different reasons: the Liberal-Democrats have always favoured proportional representation over the current "first-past-the-post" system, and the Conservatives want to limit the number of MPs. The Bill had its first reading in the Commons in July last year and is now nearing its final hearing in the Lords.
However, the Political and Constitutional Reform Select Committee commented "The Government has declared that the Parliamentary Systems and Constituencies Bill is intended as a "major step" towards restoring people's faith in Parliament. The Government's failure to consult on the provisions in this Bill risks undermining that laudable intention."
The Lords debated for a whopping 20 hours last night and today, requiring overnight arrangements in the House, amid accusations that the Labour party were deliberately obstructing the Bill.
You can get a Lord's eye-view at their blog.