Online encyclopedia yesterday announced customers would no longer be able to access its full site unless they are prepared to cough up a monthly fee.

The site, which has been completely free to visitors since its introduction in October 1999, will now charge a $5 per month or $50 per year subscription fee.

"We are investing heavily in the content of the encyclopedia to stay on the current edge of knowledge," said Ilan Yeshus, chief executive of

Britannica may have to prove to customers that it is providing an improved service before people will be willing to pay for a previously free reference tool.

"The subscription fee will mean we can update the site more regularly and that's not just from a content point of view," said a spokesperson at Britannica. "We can develop the site to make it easier to use and better to find information. But we have also added an archive of new articles and Webster's thesaurus."

The site will still include a range of free resources for basic reference material, and the first paragraph of all information will remain free. Britannica insists this was not a way of making people pay, but instead "allowed them to read the basis of the article before they paid for it".

"For the past two years has been one of the most popular sites on the net and has enjoyed the loyalty of millions of regular users," said Yeshus. "Those people have told us what they want in an online reference service and we have created one that I believe will meet their needs."