Whilst there is income tax on "income", it's possible to have an "income" of £25k-£30k without paying income tax. Just a matter of planning.
The first £12.5k is tax free due to the personal allowance.
The first £2k of dividends is tax free as it's within the 0% dividend tax band.
The first £1k of interest is tax free as it's within the 0% interest tax band.
The first £1k of casual self employed work is tax free due to the trading allowance.
The first £1k of casual property income is tax free due to the property allowance
No NIC on any of that either (currently).
If you've an investment portfolio, you can sell shares each year to produce a capital gain (i.e. profit) of £12.5k covered by the annual capital gains tax exemption. (So you put your investments in capital growth funds rather than income funds to "create" a capital gain and "sell" a portion of your portfolio each year to hit the £12.5k!).
That's £30k completely tax free. And that's before investments/savings held within ISAs which are also tax free in terms of both income and capital gains.
(I'm deliberately not mentioning the additional £5k personal savings allowance because of the complexity, but basically, someone could have an income of £35k if their "split" of income/gains is properly planned out so optimised into the different categories of income).
Obviously people also pay other taxes, such as VAT, fuel duties, tobacco/alcohol duties, etc etc. but I'm just talking about income tax.