[wpietri]

I don't know how the UK does it, but the rule in Mexico is that people without work visas can't do anything people normally get paid for. I think that's to minimize shenanigans. "No, officer, I just wait tables here for fun. Nope, no pay. Why would they pay me?"

[theorique]

That seems to be a strange criterion.

The waiting tables example is "obvious", and while some activities are only compensated for a small elite (playing basketball, musical performance), there are a lot of activities that might be compensated and might not. Or be compensated indirectly.

For example, speaking at an academic or professional conference is "work", but it is probably not compensated (except possibly for a keynote or lead speaker). An author giving a book tour is work, but they are not getting paid for talks - instead, they may be "paid" in greater exposure for their work and possible increased sales.

[Nursie]

I know there are specific exemptions for some stuff in the UK - tech support is one of these. If you have sold hardware or software to a UK company, you're allowed to come into the country and fix it with no special visa. Anything other than directly fixing the problem would be considered consultancy and a visa violation.

There are some other exceptions but most work or work-like activities you'd need a visa of some sort for.

[unwind]

So if I go to Mexico, I can't code for fun on my laptop? I hope that's not the case.

[wpietri]

You can code for fun, but my understanding is you can't do it for a Mexican entity. E.g., if you're hanging out at cafe and say, "Hey, let me make a website for you guys," that would be illegal. Actual enforcement varies, of course.

[mynegation]

You can, but you should not be paid for that by Mexican company or individual