See figure 1.3a - https://www.gov.uk/government/publications/migration-advisor...
Note that to the best of my knowledge, these numbers don't include the Afghan resettlement scheme which would further lower the proportion of employment driven visas.
Who indeed will pick the cotton.
Progressives (in the US at least) generally support immigration with protections and fair wages. They also recognize, rightfully, that systems built for decades upon exploitative practices (low wages, no protections) if removed overnight will cause mass disruption of those systems.
Neither of these is in any way supportive of slavery, modern or otherwise. The first - suggesting that immigrants be treated civilly and paid a living wage - has been fought tooth and nail by 'free market' literalists. The second - that there will be disruptions in social and economic systems when an entire workforce is suddenly removed from the systems that it has propped up for decades - is common sense and historically founded.
You're conflating these things to try to justify a talking point that was just created three months ago.
Like, come on now. Give me a break. This type of reasoning is so caked with bullshit I don't think anyone on the right even buys it.
Sure, we can say maybe the left is arguing for exploitation, but certainly the right aren't champions of human rights. I mean, what's the big picture here? "Don't exploit the immigrants! Instead, violate their rights and force them into camps!"
We can solve the immigration problem overnight, if anyone cares. Just say that if you're found hiring undocumented people, you go to prison. I garauntee you, the problem will solve itself with such expedition it will leave you in awe.
But nobody on the right actually proposes this. Because they don't actually care about immigration. They care about populist messaging. They want you to believe there's an enemy within causing all your problems, and they they alone are the solution.
But no - they, too, directly rely on the exploitation. They won't ever patch it. It will always be lip-service, propaganda, and populist messaging.