The Guardian article you link is simply reporting on the Wikipedia vote from a couple of years ago. Wikipedia keeps a unreliable sources list, and a perusal of

The Guardian article you link is simply reporting on the Wikipedia vote from a couple of years ago. Wikipedia keeps a unreliable sources list, and a perusal of it will show you that it's not an impressive exercise in fairness. In fact, Wikipedia's fairness standards are somewhat notorious. As a minor funny/sad side point to all this, Peter Hitchens over at the Mail on Sunday -- owned by the Daily Mail, but with a separate editorial team -- has complained frequently about his Wikipedia page being defaced by this very policy. Apparently some enterprising editors thought that it was their duty to remove all Hitchens quotes from the article because his articles had appeared in the Mail on Sunday, and was therefore an "unreliable source" despite being a quote of what the man said. What a shitshow! My own guess, as a sometimes Daily Mail reader from the States, is that the "unreliable" thing is simply a talking point somehow related to UK politics. The Daily Mail has a severe sensationalist bias, but their reporting is often quite good, and they have more than their fair share of scoops.