No to all of the above. In most countries (including the UK) having a company registered doesn't mean you are also actually running a business and are being treated as self-employed (and loose typical employee benefits). It would be nice if people actually read up on the subject matter before spreading a whole bunch of FUD. Having a business registered and actually creating your primary income from it, are two entirely seperated things from the tax collectors' perspective. In the end the government is not going to waste time & effort on doing all the accounting for companies that have a revenue which is close to zero.
I've had (and still have) a company registered in the NL for over a 25 years already while being employed, working on the side, being laid off (due to employer bankruptcy) and being self employed so I've been in all the situations outlined above and having a company registered never got in the way of anything. Never paid a dime for accounting fees as well.
nctnico - that (in the UK) really depends on how you set up your business. And you have to make and file accounts. And NI payments are very different if you are a registered company director - or an employee. And most regulation is based on "self reporting" - so if you do not report they do not react. But in case of problems they will turn your life upside down. You can mark your company as "non-trading / inactive / dormant " and avoid a lot reporting apart from periodic confirmation statements - but then the company is not allowed to do anything (on paper) - but you still have to file the statements.
And regarding employment while having a company - well - you might have been lucky. If a company goes through a redundancy round - they will use any excuse in the book to get rid of you - especially in place where it is hard to get rid of people. So having a company thereby potentially "voiding" your employment contract can be an issue.
You are welcome to discuss the nuances with my wife who is a corp tax director as well. It is NOT without personal risk setting up a business.
I have owned and managed large companies across Europe. I have had permanent staff in SE, DK, UK, DE, FR, NL, IT, ES & PT. And from the list - NL & DK are the most "liberal" regarding self employment vs employee. UK not far behind - but UK again is more based on self reporting than snooping (still). And HMRC is very segregated between Personal and Company.
And as "Nominal Animal" wrote - in FI you class as entrepreneur if you setup your own business, potentially limiting your access to benefits.
So the risks are very dependent on the country you live in. And having a registered business CAN be a breeze - but it can also be a pain - especially in the more bureaucratic countries.
It can also impact your personal credit rating if you have a company with very little throughput. Companies like Experian match your company registration with you - move your credit rating based on your company performance (and all the other data they have about you)
So like everything in life - there can be complications.
So I'm all for people setting up companies - but do NOT do it without prior advice from an accountant who knows your situation including your personal situation. Check your employment contract - and check with your employer if they are ok with it if it breaches your employment contract. Get it in writing if they approve. Check the papers you need to file annually and ask the accountant if you can do them yourself - or if someone has to file on your behalf (like an accountant)