So, this may be different in the UK, but in the US a large majority of travel occurs in private cars, so omnipresence of ALPRs is close to collecting data on everybody and knowing what everybody is doing at all times.

One might assume from a game-theoretical perspective that this is no different from living in a village where essentially everyone knows everyone’s business, and the knowledge that that knowledge is mutual prevents people from acting badly with the information that they have. However, in the situation where a small minority of people have knowledge about everyone else, and not vice versa, this can give that minority unearned power over everyone else.

In practice, it doesn’t feel great. I hope this answered your question.

There are two key concerns:

1. Data is retained by a handful of companies. If it is leaked, you'll have a lot of information on people that is suddenly fair game for anyone including insurance companies, PI, home invaders.

2. In the US, I'm not concerned about local government as much as federal when it comes to the fourth amendment. Suppose you have a rogue potus. He sends the national guard in to Atlanta, Chicago, and Downingtown to take over the systems of these companies. Now you say, "well I'll just remove my license plate!" But these companies are cataloguing make, model, color, bumper stickers, dents; so you can take off your plate in a situation like that but they are going to still be able to track you with a high degree of certainty. People were shocked by South Korea declaring martial law -- we've become so spoiled taking these essential laws for granted. (Sorry I don't know enough about British law.)

If they don't send all license plate data to the internet there isn't an issue. But they do.

Reconstruction of social networks via physical movement metadata.

At the fictional extreme, https://news.ycombinator.com/item?id=43817664#43818003

No shortage of non-fictional steps along that path.

I think it’s reasonable to refer to a query of a database as a “search” as in “searches and seizures”. In that context, the gathering of data should be okay if a given search of the data requires a warrant. Unfortunately, warrants are only required for ”seizing” the data, not “searching” what has already been seized. Given that, it is reasonable to refer to the collection of data as a privacy violation especially given the breadth and scale of such a collection.

The agreeable arguments I hear tend to make the case that the scale is the problem. There’s a huge qualitative difference between having a human officer tail a human suspect to track the latter’s movements in public because that person is suspected of having committed a crime versus tailing via automated machines everyone in the vicinity at all times for no reason other than “nobody said we can’t”.

You'd need to look at it from the lens of whether it constitutes a search.

IJ is the real deal. Check out their dossier of Supreme Court wins. It will be interesting to see what the eventual Supreme Court arguments and opinions are.

In that instance they had a one way entrance and exit, so I drove out the entrance. My policy now is to drive through an ALPR, mark it on OsmAnd, then go a different route.

Google street view is helpful, though these things are going up at an alarming rate. There's also a website that has a list, though it isn't maintained (e.g. there are hundreds of these near me but none are on that website).