The education secretary, Alan Johnson, has come under fire for recommending the use of the free online encyclopedia Wikipedia for schoolwork.

Wikipedia, which launched in 2001, is written by volunteers. Anyone can edit or add to entries, which means the potential for misinformation is huge. In January, the site had roughly 7m entries, in 251 languages.

Mr Johnson described the internet as an "incredible force for good in education" at yesterday's annual conference of the National Association of Schoolteachers and Union of Women Teachers (NASWUT) in Belfast.

"Wikipedia enables anybody to access information which was once the preserve of those who could afford the subscription to Encyclopedia Britannica and were prepared to navigate its maze of indexes and content pages," he said. "Modern technology enables a whole range of new educational tools to be used by pupils, teachers and schools."

But teachers and the website's founder, Larry Sanger, criticised Mr Johnson for encouraging pupils to use the website.

The general secretary of the NASWUT, Chris Keates, said the union itself had been the victim of scurrilous claims on Wikipedia. She said the online encyclopedia was popular but she would not recommend it to children as their sole source of information.

Wikipedia is among the top 10 most visited sites on the internet but it has been dogged by concerns in recent weeks over the veracity of its information. In March, a prominent and longstanding Wikipedia contributor was revealed to be a 24-year-old college dropout.

Mr Sanger, one of the founder members of Wikipedia, left the site after concerns for its integrity. He launched a new online encyclopedia - Citizendium.org - two weeks ago, which will be monitored and edited by academics and other experts as well as accepting public contributions.

Mr Sanger said the aim of the new resource was to avoid the inconsistency and potential for vandalism of Wikipedia while retaining its democratic ideals. Volunteer contributors to the new site will be expected to provide their real names and experts in given fields will be asked to check articles for accuracy. Approved articles will receive a green tick to indicate their reliability.

Universities have long questioned the reliability of information posted and edited on Wikipedia. Marketing officials in UK universities monitor the information on the site because it can affect institutional reputations, acting as an alternative university guide.

Some American colleges have gone a step further and banned undergraduates from citing the website in their research papers. Middlebury College, in Vermont, proscribed citations from Wikipedia in January.

UK universities could well take similar measures, predicted Will Murray, director of a plagiarism advisory service for British higher education.

"There's a general feeling that students are regarding Wikipedia as an authority without checking to see if it is or not. It's a site that should be treated with scepticism and it's those skills that higher education is interested in getting across to students," said Mr Murray, of the Joint Information Systems Committee (Jisc).

He added: "There's a temptation to use the internet rather than peer reviewed journals. [Studnets] need to have a critical eye."

Jisc's TurnitinUK software is used by 90% of UK institutions to detect student plagiarism. The software can also detect plagiarised words on sites such as Wikipedia and identify where they came from, he said.