found it
the paragraph below says:
"If you were looking to get a comfortable post-tax income of £26,000 a year and wanted to get a guaranteed income paid to you via a joint-life annuity, you'd need a pot of £265,420, according to our calculations. This also factors in receiving annual state pension of around £16,000 as a couple, so you'd need to generate annuity income of around £10,000 per year."
so the sum appears to be, a pot that will generate £10,000 p.a. in addition to your two state pensions.
Which is less than 4% p.a.
(pretty poor rate, considering you have handed all your money over and will never see it again)
It is often said that you can take 4% p.a. from an investment account without the fund shrinking, because income plus growth can be expected to equal or exceed what you are taking out.
The returns on joint-life are lower than on single life, because the chances of one of you living to a hundred are doubled.
The Which? article is very badly worded.
IMO you would do better with income drawdown or partial encashments.
From their figures, they seem to be working on round about 6% from income drawdown, I can't get the exact figure, but very similar to my estimate.