The Safety of Rwanda is quite broad but as per the opinion of legal experts it still leaves some routes for appeal:
Section 4(4) goes on to provide for very limited circumstances in which a court can grant an interim remedy to prevent or delay someone’s removal to Rwanda. Such an interim remedy can be granted “only if the court or tribunal is satisfied that the person would, before the review or appeal is determined, face a real, imminent and foreseeable risk of serious and irreversible harm” if removed to Rwanda. (Incidentally this is similar to the test for interim measures applied by the ECtHR.)
These grounds of challenge are obviously designed to be as narrow as possible. However there is no doubt that such challenges will be brought, possibly in large numbers. Whether any claim succeeds will obviously depend on the strength of the evidence about a person’s individual circumstances and the risk they might face if removed.
The other possible route of challenge is to the ECtHR in Strasbourg. Again the argument would be that the Act, or a particular decision under it, breaches a claimant’s ECHR rights. A claimant would be expected to bring such a claim only once any claims in the domestic courts have failed. The ECtHR will not be bound by the UK legislation or by the presumption that Rwanda is “safe”. It will conduct its own assessment on the basis of the evidence before it.
When passing the Act, why didn't Parliament close all routes for appeal and make it completely impossible for any court to intervene in any manner whatsoever into the deportations? There has been a lot of debate in Parliament over this Act so I expect the answer to exist in one of the public debate transcripts.
I’d expect them to pass a law saying something like “no domestic or international court may delay or stop a deportation to Rwanda” but the actual version is quite a bit weaker.