In the US, something has to explicitly be made legal to be permitted. There has to be a law saying you have the right to do something.
In the UK, something has to be specifically forbidden by law, and even then it's very unlikely that such a law will ever be enforced unless you're really making a nuisance of yourself.
In practice that's not something I'd bet my not-being-in-jail on in either country. Whatever foundation of "anything not forbidden is permitted" has been crusted up with so many layers of governmental power grab that whatever the theory may be, the practice is that if it is not explicitly permitted it is forbidden, and the only reason things not explicitly permitted are allowed is because they just don't happen to make a fuss about it today.
Well that's just flat-out incorrect.
This makes fair use an affirmative defense, which is default risky because the process starts with somebody accusing you of wrongdoing (potentially criminal wrongdoing).
Indeed more so, the UK has nothing as wide ranging as US Fair Use, just a much more narrow list of permitted allowances.
One of the reasons that some members were opposed to the bill of rights was because they were afraid that the population would take it as a defining list of things they were allowed to do, as opposed to the stated: "The Powers not delegated to the United States by the Constitution, nor prohibited by it to the States, are reserved to the States respectively, or to the people."
This means you can't rip an audio CD, DVD, or bluray, even if you don't have to bypass DRM to do it.
I'd expect this translates to even dumping your own ROMs/ISOs from cartridges or discs you own, too.
A huge chunk of the population ignores this, but it's another fun thing for Nintendo et al to hit you with, if they so desire.