The interest is understandable. From a standing start in 2001, Wikipedia will notch up about 2.5 billion page impressions this month. Traffic is doubling every four months and, as the site makes its transition from hippy-esque experiment to serious media proposition, two very different views about Wikipedia are emerging.

For hard-core “Wikipideans”, it is one of the wonders of the internet age — a massive, charitably funded repository of knowledge, compiled by volunteers whose aim is to create versions in all the languages of the world.

For John Seigenthaler, the founding editorial director of USA Today, who discovered he was linked to the assassination of President John F. Kennedy by a libellous Wikipedia article in November, it is an irresponsible haven for “volunteer vandals with poison-pen intellects”.

Wales concedes that the Seigenthaler entry was the “worst” article on Wikipedia — “not the only bad article on Wikipedia for sure, but . . . the worst”. Yet although he “worries a lot about how to make sure that articles on Wikipedia are right”, he says that the rest of the work on the site “is actually pretty good”.

According to a study this month by Nature, the scientific journal, Wikipedia is as reliable as the venerable Encyclopaedia Britannica — the standard to which it aspires. The report, Wales admits, came in the nick of time — just as the Seigenthaler affair threatened to blot Wikipedia’s reputation.

“It was good to have this thing out there that said it’s not just this crazy place on the internet where people just post nonsense,” Wales says.

The cautious thinking is typical of Wales. Never mind the Nature commendation, or that the site now carries more than 2,500,000 articles and has 80 language versions. “If what you are after is ‘Who won the World Cup in 1986’, it’s going to be fine,” he says. “If you want to know something more esoteric, or something controversial, you should probably use a second reference — at least.”

Jimmy Wales, it turns out, is a very reasonable revolutionary. A finance graduate, he ended a six-year spell as a futures trader in Chicago in 2000. According to one report, he earned enough money in the commodities markets to “support himself and his wife for the rest of their lives”.

Wales says that this is true, but only because he “lives in a normal house and drives a Hyundai”. Now 39, he is the head of the Wikimedia Foundation, the non-profit body that owns Wikipedia, but works unpaid. The foundation employs just three people to carry out its mission: to provide every person on Earth with a free online encyclopaedia. The real work, after all, is done by the site’s army of volunteer writers.

The mix of ultra-low overheads and huge readership would excite any media executive. And although the site does not carry advertising, Wales admits that it might. “There is a great deal of resistance to the idea, both from the community and from me,” he says. “But at some point, questions are going to be raised over the amount of money we are turning down.”

However, commercial companies have so far blundered in their efforts to cash in on the Wiki craze (the name is derived from the Wiki Wiki or “quick” buses found in Hawaii). A Los Angeles Times “Wikitorial” experiment was flooded with obscene material. “The point I would make,” Wales says, “is that they chose the most difficult thing there can be to write collaboratively: opinion . . . on the Iraq war.”

That may not be Wikipedia’s only limitation. Wales says that the fallout from the Seigenthaler affair gave fresh impetus to plans to close articles to public editing once they have been “checked”. The site is to test various methods of reviewing articles — including sending them to sets of experts — to judge whether they meet a “Britannica or better” standard.

However, Wales also admits that if Wikipedia starts to close articles, its core claim to be the encyclopaedia “that anyone can edit” will ring hollow. Here is the nub of Wikipedia’s own identity crisis: can the site stay open and authoritative at the same time? If Wales can find a solution to the conundrum, he really will have come up with a set of answers worth a closer look.

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