Google has defended itself against criticism from EU authorities over how long its keeps hold of visitors' personal information.

A recently published EU report has stated that there is no reason for search services to keep personal data beyond 6 months.

Google currently has a policy of retaining data for up to 18 months.

It claims in response to the report that this is necessary to improve search results.

The report, by the Article 29 Working Party, accompanied a new set of recommendations for how European data protection laws should be applied to web search services, which is now available to view online.

The Working Party is calling for online search users to be warned about how their information is being used; and that web companies that do not do this should face legal consequences.

"It is the opinion of the Working Party that search engines in their role as collectors of user data have so far insufficiently explained the nature and purpose of their operations to the users of their services", the report states.

"The Working Party does not see a basis for a retention period beyond 6 months", the study concludes.

Peter Fleischer, Google's global privacy counsel, responded: "We believe that data retention requirements have to take into account the need to provide quality products and services for users, like accurate search results, as well as system security and integrity concerns".

Google's response also argues that IP addresses should not be viewed as personal data - while the EU authorities say they should.

The debate continues.