The chancellor’s response is expected on Nov. 25, when he will set out a fiscal strategy to eradicate the deficit and bring Britain back into a budget surplus by 2019-20. As part of this, Mr. Osborne will indicate how he plans to alleviate the pain that his tax credit cuts will cause.

Image A video image of the House of Lords debating the government's plans to reduce tax credits, last month. Credit... Press Association, via Associated Press

What is astonishing is that a mutiny by a legislative chamber without a single elected member could command such a change of course. The closest the House of Lords gets to democracy is when its 821 members vote to choose a new hereditary peer (most are appointed for life, and cannot pass on their title or their seat in the chamber to an heir).

This arrangement was in itself the result of a trade-off both bizarre and entirely in keeping with the curious history of the House. In 1999, the hereditary lords were expelled from Parliament by Prime Minister Tony Blair — only for some to be readmitted by an internal election process. Today, there are 88 such “excepted hereditary peers.” No less remarkably, 25 Church of England bishops are entitled to sit on the red benches of the House.

Of the remainder, the life peers, who are a majority in the House, some are nominated by the main political parties, while others are selected by a parliamentary commission from the nonpartisan pool of people who have gained distinction in the professions, academia or science.

How, in 2015, can one defend an unelected club forming part of the legislature — a heritage site masquerading as a modern institution? With difficulty. Back in 1912, Prime Minister Herbert Asquith declared that an overhaul of this constitutional dinosaur would “brook no delay.” Yet delay is all there has been.

Every time the Lords blocks a government initiative there is fresh talk of reform, a radical plan to install an elected senate. In 2012, the Conservative-Liberal Democrat Coalition proposed a mostly elected body, with a much smaller membership, and 15-year terms.

But this new, democratically legitimate Upper House represented a threat to the supposed primacy of the Lower House. And thus Conservative rebels in the Commons thwarted the bill — triggering the worst political crisis in the Coalition’s five years.