Semi-related question: How do you calculate taxes in UK? Is the base of the tax the salary offered by companies in job offers? I mean, with say £60k job offer, do I pay tax from £60k? (with the last £17k being taxed at 40%)?
Nope, you pay tax on the full amount. Each taxpayer has a personal allowance (currently £11,000 generally, but this varies) on which no tax is paid; a rate of 20% applies to income between £11,000 and £42,000, a rate of 40% on income between £42,000 and £161,000, and a rate of 45% above that.
I mean, for example in France, the salaries might be advertised as "€35k", but from this you deduct social charges etc., and you pay tax from the "taxable income" which would be for example "€27k". Does this work the same in UK, or do I pay tax exactly from what the job offer says?
In the UK you pay National Insurance (NI) on your gross earnings. NI pays for things like the National Health Service. The amount you pay depends on your employment status and how much you earn [2]. I assume this is similar to "social charges" in France.
After deducting NI and the tax-free allowance [3], you pay income tax on whats left. And whats left after that is yours to keep.
Most regular employees have tax and NI automatically deducted from their monthly/weekly pay by their empoyer. This is called Pay as You Earn (PAYE) and keeps things simple. Company owners, contractors, etc. often pay tax yearly or half-yearly and often employ an accountant to arrange this.
[1] This is the amount that the job pays, before all taxes and deductions.
