A remedy against affection for the House of Lords is to try explaining it to foreigners. Like a senate, you say, but the members are mostly appointed by party leaders. (Your listener’s eyes narrow with suspicion). Except some still inherit seats in lines of aristocratic succession. (The eyes now widen in astonishment). Oh, and the bishops.

How long is a term? A lifetime. But when new members are added, doesn’t that mean the chamber just gets bigger and bigger? Yes. Yes, it does.

Today, we learn that Theresa May intends to shovel a few more Tory bodies into the upper house because it isn’t doing what she wants it to do over Brexit. And because she can. Try that one on a puzzled outsider: the head of a UK government, facing obstruction in parliament, can rearrange the allocation of seats with a stroke of her pen. (Opposition is bought off by letting Labour appoint a few peers, too. So what would be a wild affront to democracy tilts towards bipartisan stitch-up.)

There are two defences for such preposterous arrangements in the 21st century. One is that it works in spite of the anachronism and the other is that it works because of the anachronism. Peers have a healthy detachment from the partisan frenzy of modern politics, but awareness of their tenuous mandate also provides healthy deference to the Commons. By some mysterious alchemical process of culture and history, elements that should combine to make a sulphurous undemocratic stench make, instead, legislative gold.

The persistent liberal itch to reform or scrap the place subsides when peers perform what look like noble public services. So it has been with the EU withdrawal bill. Remainers cheered as the Lords rewrote statutes so they now instruct the government to seek a much softer Brexit. Hardline Eurosceptics are appalled. A caravan of political ironies troops past: pro-EU Liberal Democrats who tried and failed to reform the Lords now cherish it as civilisation’s backstop. Reactionary Tories who thwarted change to the upper house now denounce it as democracy’s nemesis.

May’s new appointees will be ermine-clad in time for the next Brexit battles – and there are plenty. The withdrawal bill hasn’t finished its parliamentary journey. There are customs and trade bills in the pipeline. Last year’s Queen’s speech promised Brexit-specific laws on fisheries, agriculture and immigration. In the autumn, parliament is supposed to vote on a motion endorsing the withdrawal deal that May negotiates in Brussels (presuming she gets one) coupled with a statement of intent describing the apparatus of future trade with the EU.

The withdrawal agreement then has to be approved as primary legislation in its own special “implementation bill”. There will be a lot of voting on a lot of law, even before the amendments start flooding in. The safest prediction is that it isn’t going to be pretty. Nor will it always be obvious to anyone but the nerdiest aficionado of parliamentary procedure what precisely is going on.

Most of the action will be in the Commons, in the long shadow of May’s failure to secure a majority last year. But the Lords will be crucial. I get the impression from talking to peers on all sides that there is very little appetite in the upper chamber for outright wrecking of Brexit. Or, rather, there are many Lords who would gladly stay in the EU, but none who believe their chamber can take that decision on behalf of the nation. There is a feeling that the constitutional duty to scrutinise and improve legislation can be stretched quite far – as with recommending a Brexit very unlike the one May is currently proposing. But to overturn a referendum result would stretch the elasticity of the mandate well beyond its breaking point. The message from most pro-remain peers is that, without an obvious shift in public mood, they’ve done about as much as they can without sparking a full-blown constitutional crisis.

Ministers know that, too. They do not think the Lords will block Brexit, but they are fed up with parliament – either chamber – meddling in the whole process. And since May can’t rewrite the numbers in the Commons, astroturfing the Lords with friendly fans is the best she can do.

The stopped clock of the upper chamber has told the right time, as inevitably it does, but that doesn’t mean the mechanism behind the archaic face is ticking and whirring in healthy fashion. The hands might often point in ways that liberals admire, but to follow that logic towards admiration for the system is a perilous path. It is an invitation towards patrician weariness with the cacophony of electoral politics. In the age when Donald Trump can capture enough of the popular imagination to seize power in a constitutional republic, it is tempting to find comfort in the ponderous, temperate machinations of the least modern place in parliament. That impulse feeds on nostalgia, not for feudal times but for a more recent past, when politics and the world seemed less frantic, less volatile, less hysterical.

The House of Lords is certainly not hysterical. But it is still ridiculous. And that doesn’t stop being the case just because it sometimes does the right thing.

• Rafael Behr is a Guardian columnist