Not directly answering your question, but there is massive conflation in the public debate between "illegal immigration" and "boat people asylum seekers".
Several institutions suspect that the population of the UK is larger than the official figures but driven by visa overstayers who initially entered the country on a legal visa and then disappear into big cities, working gig economy or under-the-table jobs in their communities.
It's somewhat possible to predict which types of visa lead to that profile of person most likely to overstay - and it's things like work visas for lower-skilled jobs and study visas for non-selective institutions. This includes the well-known case of people coming in on care worker visas and then never actually doing care work, or doing a few shifts then vanishing.
This is literally "illegal immigration" and isn't linked at all to asylum-seeking boat arrivals, which is technically a "legal" route (on paper - I'm not commenting on the desirability of it).
It's also well-coordinated with e.g. "agents" who recruit "students" who all know full well that they're paying for a visa not an education.
In 2024 around 800k visas were issued across work and study routes.
Increasing the selectivity of these legal routes decreases the % of the people who overstay and become illegal immigrants - who might not get free hotels but who increase pressure on services/housing and usually don't contribute via taxes.
It's not good enough to just say "oh well working and studying are good things so no problem here".