The ESRB has re-rated Bethesda's acclaimed RPG title Oblivion, following the discovery of a third party modification that adds female topless nudity to the game - but the UK's BBFC says that its 15 rating of the game remains unchanged.

"Were it the case that the developer themselves had included and failed to disclose certain modifications of content, a recall may be required," has declared BBFC spokesperson Sue Clark, "but not as a result of a patch that has been placed on the Internet by a third party."

In the US, the Xbox 360 and PC title was initially rated T (Teen 13+) and carries a standard ESRB description of Violence, Blood and Gore, Sexual Themes, Language, and Use of Alcohol. As a direct result of the third party modification available from the Internet, the game will be re-rated as M (Mature) and the PC version will carry an additional description for Nudity.

Developer Bethesda has stated that it will adhere to the decision made by the ESRB, and is currently working on placing M-rated stickers on current warehouse and retail packaging, with future PC copies all carrying the new rating sticker as standard.

According to the ESRB, the content which caused the rating to be changed "involves more detailed depictions of blood and gore than were considered in the original rating, as well as the presence of a locked-out art file or "skin" that, if accessed through a third party modification to the PC version of the game, allows the user to play with topless versions of female characters."

Bethesda said that it stood by its original submission to the ESRB, denying charges that either it or publisher Take Two Interactive - which also published Grand Theft Audo San Andreas, which was controversially re-rated last year - had hidden anything from the ESRB.

"Bethesda Softworks made what it believes was a full, accurate, and comprehensive submission on Oblivion to the ESRB months before the game's release. Bethesda used the ESRB's application forms and believes it adhered closely to their requirements. Nothing was hidden from the ratings agency."

"There is no nudity in Oblivion without a third party modification," Bethesda continued. "Bethesda didn't create a game with nudity and does not intend that nudity appear in Oblivion."

In terms of the alleged excessive violence cited by the ESRB, Bethesda added: "We advised the ESRB during the ratings process that violence and blood effects were 'frequent' in the game - checking the box on the form that is the maximum warning. We further advised that the game contained occasional torture, vulgar acts, and gore. We gave accurate answers and descriptions about the type and frequency of violence that appears in the game. We submitted a 60-page document listing the explicit language, acts, and scenes in the game."

The BBFC appears to agree with Bethesda:"the BBFC is extremely thorough in its evaluation of products and insists on full disclosure of all content in the game before issuing a rating. What we have classified as 15 is the product that you can buy in the shops, and any modifications to that product afterwards by a third party fall outside of the powers of the Video Recordings Act."