Jack Straw, the foreign secretary, makes surprise visits to Ilford instead of Iraq and Robbie Williams earns his millions eating pet hamsters. Oh, and David Beckham was a Chinese goalkeeper in the 18th century.

Cyber warfare has broken out on the online hip alternative to Encyclopedia Britannica where people are free to contribute their own articles and revise any of the existing 2.5m entries.

Hackers are abusing this openness to vandalise the site so frequently that its gatekeepers are relying on a volunteer army of nearly 1,000 supporters to police and correct the entries.

Last week the 19-page entry for the prime minister was being changed as many as 25 times a day. He was briefly accused of having posters of Adolf Hitler on his bedroom wall as a teenager and of starting a “false” war against Saddam Hussein.

One saboteur, codenamed Thruston, changes the same sentence in Blair’s entry on an almost daily basis to accuse him of setting out to “destroy” civil service neutrality.

The organisers of Wikipedia last week launched an investigation to see if any of the postings are coming from the House of Commons. It follows the discovery that some insults about American politicians posted on the site originate from offices of their rivals at the Capitol building in Washington.

Wikipedia was set up five years ago as a non-profit enterprise, designed to provide almost real-time biographies and a people’s version of history. It has only three full-time employees to vet people’s entries, relying on the near-1,000 enthusiasts to correct vandalism quickly.

Even if the insults are removed in minutes, however, they can still be read by anyone logging on and viewing the history of updates. It means the encyclopedia, based in St Petersburg, Florida, has now notched up 2.5 billion page impressions in 80 languages.

Dedicated “Wikipedeans” regard it as a massive repository of knowledge which can be updated in an instant. Others, however, see it as the online equivalent of throwing eggs.

John Prescott, the deputy prime minister, has his own antagonist who regularly insults him with such epithets as “fat bonehead”. The caption under a photograph of Prescott was changed to read Rhubarb Pie.

Another hacker regularly removes whole sections of Gordon Brown’s biography and replaces it with one word: “tax”.

The postings encompass all parties. David Cameron, the Tory leader, was described as a “bitch” last week. Mark Oaten’s entry was updated within an hour of news breaking of his resignation from the Liberal Democrat front bench over a rent boy scandal.

It is not just politicians who suffer. The Duchess of Cornwall’s Christian name was altered to Cow-miller and her title to Her Un-Royal Lowness.

Enemies of Sienna Miller, the actress whose on-off affair with Jude Law has captured tabloid headlines, dispute her height and claim that she has modelled nude. An entry for Robbie Williams, the singer, last week read “. . . makes his money by eating domestic pets in pubs in and around Stoke”.

Wikipedia is now planning a fixed version of its encyclopedia which cannot be changed.

Jimmy Wales, 39, founder and president of Wikipedia, said he had expected vandalism to have been greater. “I thought it would be overrun with idiots but there are far more people doing good than those who try to be harmful.”

He added: “We have now got people looking at the identity numbers of people changing entries about British politicians to see if any of them have come from the Commons. We think it’s funny when we see the source of something and one senator’s office is editing to call another senator a douche bag.”

Explore UK News

• Crime News

• Education News

• Health News

• Scotland News

Times Recommends

• How I lost the gift of joy for a while
• Why Ann Widdecombe has got it wrong
• Alas, it’s the end of the road for petrolheads