It's more or less inevitable that this will go to the Supreme Court, especially when it's a 2-1 majority opinion rather than unanimous.
Still reading the judgment (linked below), and may comment further afterwards on the specifics, but since this is surely not the end of the story of whether the policy is lawful, it's probably better to wait for the end of the legal process before discussing further action.
I will, though, say as a general point that it's almost inevitable that Human Rights are only visibly relevant for the most vulnerable people, ie (in this case) asylum seekers. But the principles still apply in general. And the relevant article in this case, Article 3, states that:
"No-one shall be subjected to torture or to inhuman
or degrading treatment or punishment."
How is this objectionable? And how is there any meaning to this basic protection if you can simply circumvent it, by sending somebody to another place where they may (or will) be subjected to torture, inhuman treatment etc., instead?
It's the same protection we all enjoy, and would always wish to enjoy; and, since the only qualifier to human rights is to be human, then naturally every other human should enjoy it as well. All of these are general principles. Or, at least, should be. The key is that the most basic protections apply to everybody. Not just those who the Government likes. Everyone. Without exception. If that makes things occasionally complicated, so be it.
Whether the Court is correct to find this specific policy unlawful by this measure, I don't know. But it's the right measure, and the right question, and even the Government agrees with that (although they are, for political reasons, careful not to draw too much attention to this).
https://www.judiciary.uk/wp-content/uploads/2023/06/AAA-v-SSHD-judgment-290623.pdf