I cannot confirm that. I found the tax agreements within the EU to be relatively easy in the EU & UK. Of course you deal with two authorities, so there is an additional benefit, but recognizing taxes paid in the UK with another country was not that hard.

Yes, there is no double taxation - but you essentially need to involve yourself with the tax authority of every country you are doing business in.

In a real single integrated market, I'd have company registered in country X, serve customers across entire Europe, but file taxes on the entire income in X only. I'm thinking they don't allow that because it would open doors to all kinds of tax optimization for the little people - ex. say UK workers would register themselves as companies in countries with very low taxes, and continue to work ("provide services") in UK. This kinds of schemes are allowed for the megacorps, but not for us regular folk.

"involve yourself" in this case is present the tax income declaration to the tax authority in the 2nd (3rd, etc.) country.

Hardly a cumbersome experience.

In practice, you need to learn the tax code to find most suitable form of conducting business. For example, in the UK if you know what you're doing, you'll pay ~20% tax on your income as a contractor. If you don't, you can easily end up paying something like 30+%.

Also, there are perpetual costs of having a company registered (such as monthly payments to an accounting company which handles paperwork, health care contributions etc.), so if you move around regularly between a couple different countries, you'll probably need to maintain a legal presence in each one, and thus have these costs multiplied.

> In practice, you need to learn the tax code to find most suitable form of conducting business.

That has not been my experience.