In England the health system is free to everyone, the private health insurance buys you very little.

Same in Denmark. I'm not a Danish citizen, but since I'm legally resident in the country (work/residence visa), I'm in the system. In fact since everyone is in the system, the yellow health-coverage card is de-facto used as your ID card for some purposes (there's no national ID card).

Anyone visiting the country but not resident here is also entitled to emergency care, e.g. if you fall off your bike as a tourist and have to go to the hospital, there is no charge. Same if you have a heart attack while visiting.

If I get a travel visa to England, I can get free cancer treatment?

If you are entitled to live and work in England, you are entitled to free healthcare. Since the subject is about running a startup in London, you'd have to have those entitlements. This isn't a discussion about visiting England as a tourist.

It depends!

Am I entitled to NHS treatment when I visit England? http://www.nhs.uk/chq/Pages/1086.aspx

Am I entitled to NHS treatment when I move to England? http://www.nhs.uk/chq/pages/1087.aspx

you need right of residence to register for a National Insurance number, but after that you're good to go

> health coverage isn't a major concern for 20-something hackers who sit in front of computers all day.

I wouldn't be too sure about that.

You can even be looking at having your fat exit taxed twice if you are a citizen of another country

I'm not a tax expert but I think that would only apply if you're a citizen of the USA, which is the only country in the world that taxes you on your worldwide income.

Even for the USA you'd generally not be taxed twice, because foreign taxes paid are deductible from U.S. taxes. For example if I, as an American living in Denmark, sold a startup, I would pay Danish taxes on the sale. Then I would file American taxes by computing my tax liability under the American rates and subtracting the Danish taxes paid. The result in that case would just about always be $0, because Danish taxes are higher than American taxes, so the foreign tax credit wipes out any American tax liability. If the foreign taxes were lower, you'd have to pay the difference in U.S. taxes, but not the sum of the two.

As I understand it, the US allowance for this is capped at $90k (in income, not tax paid)

There's no cap on the foreign tax credit; you can deduct millions.

What you're thinking of is the Foreign Earned Income Exclusion, which allows you to exclude the first $95,100 of foreign earned income from your taxes, if you live outside the U.S. more than 330 days a year. In my case there's no real reason to do that, because the foreign tax credit I get for my Danish taxes zeroes out my US tax liability. The main people who benefit from the $95k exclusion are those working in low-tax jurisdictions, e.g. American expats in Saudi Arabia. In their case it allows them not to avoid double-taxation (which is what the tax credit prevents), but any taxation at all.

Appreciate that correction, thank you

A lot of countries tax you if you're a resident still, even if physically non-present (Canada, etc.), and earn the income in a foreign country. You can do stuff to become officially non-resident first. that is the thing you can't do as a US citizen.