the 25% lump sum is tax free. It does not count as taxable income. It is (up to) 25% of the fund value.
Any income you take is taxable, and so is any lump sum exceeding the 25%. You have an allowance on your income before the tax starts. The treatment of income is separate from your tax-free lump sum.
https://www.gov.uk/government/uploa..._personal_allowances_and_basic_rate_limit.pdf
For example, on one of my schemes, I was not working and drew 25% of the fund value as tax-free cash, and specified that my pension income was to be 0% of fund value until further notice. So no income, and no income tax. The lump sum was enough to tide me over until things improved. Assuming that I will live to draw income from that fund one day, I will not be able to take another tax-free lump sum, because I have already had it from that scheme. The value of the remaining 75% has continued to grow. If necessary, I can turn the income tap on whenever I want. This is now called flexi-access drawdown (it used to be called income drawdown) because the amount of income you take is at your choice, it is not fixed for life like an annuity. If the fund grows by more than you take, that's great. If you take more than it grows, it will get smaller.
I also have another scheme because I have had pensionable jobs, plus what was a Personal Pension and is now a SIPP, from when I was in business on my own. I will be able to take tax-free 25% lump sums from the other schemes later. If you intend to live for a long time, or have dependents, you should be wary of sucking your schemes dry in case they run out too soon.
Because I have been in occupational schemes, I used to be Contracted Out and will not receive the Flat Rate State Pension, I will get one based on the current State Pension plus a few pence of SERPS. You can get a Pension Forecast that will tell you what you will get. If you have not already got a forecast, and a statement of your NI contributions, apply for them now.
I think WWT is talking about what they call "Take Small Cash Sums" but I have no experience of that.
You may also need to read
https://www.moneyadviceservice.org.uk/en/articles/early-retirement-because-of-illness-or-disability