Almost none, because that’s highly unlikely for most people. The system is designed such that most tax-related things don’t need a return and end of year squaring up. Income is taxed monthly by subtracting the correct amount. Interest is tax free to a threshold then has automatic withholding. Investments and savings can be held in tax-free wrappers with no reporting requirement. Benefits are paid outside of the tax system, etc.

The way it works, you get a tax code. The tax code is documented on your pay stub. The tax code changes based on things like marital status, kids, etc. The tax codes are all standard and you can easily look them up. That tax code informs payroll software how you're supposed to be taxed, and it adjusts automatically.

If you're US Based, think of it as being similar to the withholding calculation, only significantly more accurate.

I've known a few people that manually check their taxes each year, and never known them to find mistakes. Most people just don't bother.

HMRC already has the information it needs to calculate the information correctly. The same is actually true of IRS too. For almost all cases, the IRS can accurately calculate your taxes for you. In several countries, the agency responsible for taxes pre-populates your tax document for you, and sends it to you to sign off on each year. Doing taxes often involves no more than skimming through a document to verify accuracy, and mailing it off.

In the US? Plenty. I've had the gov't misattribute income before, and not in my favor.

And it's not just the gov't. I assume your employer is the one transmitting the info back to the gov't. I've had my employer miscalculate my social security tax in one paycheck.