All parties struggle to invest local elections with meaning, because no party can alter the consequences of what is coming up to two decades of austerity. They can promise they’ll work hard for local people, and many of them will, but they can’t change the maths of inadequate funding and soaring social care costs. All they can do is hope to exist in an affluent enough area.

Instead, the results are taken as a popularity contest, which – if things go your way – will hopefully supply enough buoyancy to last into a general election, and, if things don’t, will hopefully evaporate.

In other words, these are ideal conditions for party leaders to say ridiculous things, but there’s no caveat for the unbridled nastiness that came out of Reform at the weekend. It promises to deport thousands of illegal immigrants (no change there) via locked detention centres (some change there, in the direction of “warehouseification”, borrowed from Donald Trump). The kicker is, these detention centres will never be situated in areas that voted Reform, but will instead be placed in Green-leaning boroughs. Zia Yusuf, Reform’s spokesperson for home affairs, unveiled the policy with a handy tactical mapper, votegreengetillegals.com, where you can put your postcode in and see how likely your area is to vote Green and get a detention centre. It’s basically London, Brighton, Bristol and the Cotswolds, hosting as many thousands of migrants as this hypothetical Reform government can sweep up – so good luck with the real estate, guys.

As psephologists scratch around for the antonym of “pork-barrel politics” (“grotesque parody of politics”, maybe?), it’s interesting to consider who this policy is for.

It definitely will not deter Green voters, for whom the fear will not be a detention centre on their doorstep, but the existence of such detention centres, and the likely poor conditions within them, from a party that can’t organise a hanging basket, as well as the broader vindictiveness of Reform as a force in politics, will create a fresh determination to vanquish it. It is optimistic and a bit early-21st century of Farage’s party to assume that the Greens only command support in limited, metropolitan elite sort of areas, and therefore galvanising them is risk-free. But don’t interrupt your enemy while he’s making a mistake and all that.

If the announcement has an effect on the Labour party, it’s more likely to go Reform’s way. On the form of the past two years, Labour will be scrambling to meet voters’ legitimate concerns, vis-a-vis giant warehouses full of humans, drawing up plans for detention centres of its own, with elaborate PFI funding structures, fairly distributed between all the counties, so long as they are the cheapest. If this can spur the kind of craven copycat back-of-the-envelope far-right mimicry for which Labour is now fabled, there’s a chance that it will obliterate its activist base altogether.

The true message is to Reform’s own voters, though. Pointless, you might think. Why would they mind where the detention centres are, so long as they get built? If they spring up in Reform-voting areas, all the more convenient for a spontaneous protest. But the practicals are secondary. We’re not watching a blueprint for the actual detention of real-life people, but rather a “libidinal assemblage”, the summoning of strong emotions – vitriol, competition, resentment – that can then be used to shape behaviour. I’d only ever heard of libidinal assemblage on podcasts about fascism, rather than from its source philosophers (Deleuze and Guattari), and I thought, “Huh, that’s interesting. I wonder what it actually looks like?”, but it was already all around – a relentless fixation on migrants, how they should never belong, never relax, never consider themselves safe from the threat of deportation. What’s it all for? How does it create prosperity, unity, optimism? It doesn’t, because it’s not supposed to. It’s there for that little spurt of atavistic rage that will make you do a dumb thing, such as vote for the interests of capital, masquerading as the voice of the common man. The nastiness is the product, not the by-product.

Zoe Williams is a Guardian columnist