As I'm on this topic and some people seem interested, some general commentary on the UK 'immigration' politics thing. Just my own opinions, not based on any great insight.
There is certainly some popular support for more stringent immigration control in the UK. This has mostly emerged in the last 20 years or so with a couple of parties such as the 'English Defense League (EDL)', 'British National Party (BNP)' and (to some extent) the UK Independence Party (UKIP)' being formed off the back of it.
However, the topic isn't a big factor for the majority of people and so the parties remain niche. The most successful of them has been UKIP (now Reform), who attained 14.3% of the vote in 2024. Note, UKIP is the most moderate of the 3 mentioned, and also the ones least explicitly anti-immigration, being more concerned with European separation and UK independence. They gained popularity over Brexit and are now trying to remain relevant. You might say that immigration is one of UKIP/Reform voters' top 5 issues, but probably isn't number one. I expect it's not the main driver for their support either.
The others never broke 1% of the vote at any time and have basically disappeared after the peaks in roughly 2010. I'd say they occupy a similar spot to the US Tea Party or the more extreme left wing parties. They have some support, enough to get some airtime, but not nearly enough to actually have a chance of forming a government.
Also worth noting that neither major party has really touched the topic in terms of manifestos or policy. The 'moderate right wing' conservative party pays some lip service on occasion, but both parties know that this isn't an issue that'll gain them much, so they just leave well enough alone.
As for these current riots and why now, I'd attribute it to a couple of factors.
#1. the latest election has once again been a pretty comprehensive failure for these parties. They gained some of the vote (around 15% as mentioned), but due to peculiarities in the UK election system, they have attained only 5 seats in parliament (0.8% of seats).
#2. What's worse, they achieved this loss whilst Labour, the 'moderate left wing' party in UK politics, won a landslide. Labour supports none of these parties policies. At all. As such, the people who do make up these parties, especially the more fringe ones like the EDL, are feeling pretty frustrated and disenfrachised. It's clear to them that conventional political means aren't going to get them anywhere and I'm sure they're not attributing that to their lack of popular support, at least internally.
#3. It's summer and the weather is nice. Sounds silly, but nice weather and rioting are incredibly closely correlated. Guess these people care enough to go protest, but not if they'll get damp or chilly in doing so. Also, we're currently in the off-season for Premiere League Football and the UK just lost the Euros. Again, sounds ridiculous, but the demographic for a lot of those parties coincides heavily with spending their time watching 'the footie' and I expect they might not have bothered going out if it interfered with game day.
Throw in a bit of a spark in some criminal proceedings and here we are.
