LONDON — It was nearly midnight on Day 12 of the most grueling debate in recent House of Lords memory, and not all the Lords present were, strictly speaking, awake. But the Right Honorable Lord Davies of Oldham was warming to the question of the hour: a proposal to change “may” to “should” on Page 10, Line 7 of the Parliamentary Voting System and Constituencies Bill.

“If you have a criterion that says that you ‘may’ do something, that is not a positive criterion,” observed Lord Davies, a Labour peer who once worked as a schoolteacher. “It is the absence of a negative criterion. The phrase ‘may take into account’ means that, if you are minded to do so, if you really want to do so, we do not prevent you from doing so.”

Give him points for enthusiasm, at least. With the coalition government and the Labour opposition both refusing to compromise on a measure that has severely divided them, the debate had already ground on for 98 hours across several weeks. The peers are not the youngest group of people ever to populate a legislature, and after several all-nighters, some Lords were reaching the outer limits of coherence, patience and stamina.

“These are old men and women who are pretty irritated at being here when normally they’d be tucked up in bed,” said a Labour peer, Lord Hart.

Fury is more like it. The situation has provoked so much resentment here that Lordly decorum has all but flown out of the chamber’s Pugin-designed stained glass windows.

Things are so bad that when the government tried to buoy its members one night by offering a program of midnight entertainment that included talks by the “Gosford Park” writer Julian Fellowes and the former Olympian Sebastian Coe, members of the Labour Party were strictly uninvited.

“It’s never been like this before, with such a palpable sense of anger,” said Baroness d’Souza, convener of the cross-bench peers, who have no party affiliation. “I believe that if this isn’t resolved quickly, what we’re seeing is the beginning of the unraveling of the House of Lords.”

Delaying tactics

The bill would trigger a referendum May 5 on whether to change the way election votes are calculated, and it would redraw Britain’s parliamentary boundaries, reducing the number of seats in the House of Commons to 600, from 650.

The coalition government wants it, because it would fulfill the Liberal Democrats’ pledge to enact voting reform, and because the Conservatives would benefit from the boundary changes.

Labour is resisting because, while it supports voting reform, it vehemently opposes the redistricting proposal. The measure must become law by Feb. 16 in order for the May 5 referendum to proceed, and Labour is determined to delay the bill so that it misses the deadline.

Normally, opposition parties adopt a spirit of compromise and bonhomie in the House of Lords. Not this time. The government seems unwilling to budge, and Labour has resorted to virtually unprecedented delaying tactics.

These include proposing picayune amendments — more than 270 so far — discussing them for hours, and then, because they have no chance of passage, withdrawing them. While the Lords may not filibuster in the grand tradition of the U.S. Senate, they can debate until the cows come home, as long as the topic is relatively germane to the bill.

With each amendment, multiple Labour Lords rise to add their remarks to those of their companions. They reminisce about their experiences as young members of the House of Commons, discuss the rivers of Scotland, expound on how hard it is to drive around Wales when there is no cell phone coverage, talk about the demographic diversity of London and enumerate the communication problems faced by impoverished constituents without cars or computers who want to contact their legislators.

The government says that Labour is upending centuries of convention, but Labour says it has no choice.

“If you try to enact a constitutional change in this ramshackle way, without experts, without scrutiny, without study, then this is what you get,” Lord Hart said.

A House divided

The debates have been marked by breathtaking insults and accusations on both sides, with much debate focusing on the issue of whether or not the Labour members are in fact conducting a filibuster or merely robustly scrutinizing the bill.

“He must think that we are a bunch of idiots if he thinks that those of us who have been watching what has been happening are not aware that there has been a filibuster,” said Lord Lester of Herne Hill, a Liberal Democrat, speaking of Lord Falconer, a Labour peer. “In the 16 years that I have been here, I have never seen conduct like this.”

On Monday night, the deputy leader of the house, Lord McNally, a Liberal Democrat, grew so annoyed by repeated niggling questions from Labour that he began ostentatiously ripping up what looked to be the evening’s order paper. Soon afterward, he fell ill and left the chamber.

At one point during last Monday’s all-night session, Lord Trefgarne, a Conservative, drew gasps from other Lords when, saying he was fed up with the “abuse of the procedures of this house,” set in motion a procedural tool to bring an end to debate on the amendment in question — the first time such a tool has been used in 40 years, and only the sixth or seventh time since 1900.

At one point there was a long discussion about how the government had chosen 600 as the proposed new number of parliamentary seats, with Labour peers accusing the government of plucking the figure from nowhere. Some peers suggested other, random numbers, and one mathematically inclined Labour member mused on how the various figures could be expressed in terms of prime numbers.

“Perhaps I could postulate another figure, given the nature of the debate,” said Baroness Liddell of Coatdyke. “Could we maybe go for 666?”

She also said, speaking of the written transcript of parliamentary proceedings: “I will have to show my husband Hansard tomorrow to prove that at 2 o’clock in the morning I was listening to a debate about prime numbers, because he will not believe me. He will be sending for the men in white coats to cart me away.”