Arguably, most developed nations are in the same boat in terms of being able to build a bomb in relatively short notice. The main challenge is probably that refining uranium is intrinsically a slow process.
I do wonder how many supposedly non-nuclear developed countries have secret small-scale refinement plants and the ability to assemble nuclear warheads in short notice. It is the sort of stuff that they wouldn't want their own populous to know, as it is controversial.
Any developed nation _with a well developed nuclear energy industry_ would be able to build a bomb with years of effort. There's a lot that goes into a bomb beyond refining (e.g. miniturization of warhead). And to deploy the bomb a ton of work to achieve the gold standard of a nuclear triad, plus build enough bombs to be survivable past an initial strike (to maintain deterrence).
If you learn of any countries with a secret program, let your local intelligence agency know. They monitor this closely, and intervene.
You don't generally need either miniaturization, nor a nuclear triad, nor MAD. Those are only a requirement if you are defending yourself against an adversary with a ton of nuclear weapons of their own and significant nuclear countermeasures.
If that is the case, then yes, it is going to take a massive investment to build and maintain that capability, which is the reason why most developed countries don't bother. But if you only want tactical nukes, it doesn't take that much.
I could not care less if e.g. Italy, Spain or Finland have developed nukes in secret. It would not surprise me one bit, either.
The countries and territories mentioned in the broader thread need much more than tactical nukes if they are going to seek nuclear deterrence. Russia invades Spain, Spain hits what exactly with a tactical nuke? Or are they nuking Catalina? I don't see the security argument here, maybe you can detail the security interest and the scenario?
I do wonder how many supposedly non-nuclear developed countries have secret small-scale refinement plants and the ability to assemble nuclear warheads in short notice. It is the sort of stuff that they wouldn't want their own populous to know, as it is controversial.