The Internet Watch Foundation (IWF) has lifted its ban on Wikipedia, which slowed access to the site to a crawl in the UK.

On Saturday the IWF placed Wikipedia on its watch list, which it uses to alert internet service providers to sites hosting child pornography. The listing came after the site was reported to be hosting a picture of a young naked girl, which turned out to be the cover of an album called "Virgin Killer" by German heavy metal band Scorpions.

The IWF listing slowed access to the site to a crawl as ISPs sought to block it and stopped edits being made by British users. However, the IWF has now rescinded its ban.

“Following representations from Wikipedia, IWF invoked its Appeals Procedure and has given careful consideration to the issues involved in this case,” said the group.

“The procedure is now complete and has confirmed that the image in question is potentially in breach of the Protection of Children Act 1978. However, the IWF Board has today (9 December 2008) considered these findings and the contextual issues involved in this specific case and, in light of the length of time the image has existed and its wide availability, the decision has been taken to remove this webpage from our list.”

However, the founder of Wikipedia Jimmy Wales has now said he is investigating whether legal action can be taken against the IWF.

"There's no question that it's a dodgy picture, but it's an artistic protest made many years ago," he told Channel 4 News.

"But my concern isn't so much about the image. It's the ambiguous way that [the IWF] are behaving. It's not clear if they are over-reaching their authority.

"As a result of their actions, the image is actually being seen by more people, it's appearing on thousands of blogs today. It will continue to be passed on. What are they going to do? Are they going to block all of the web if it continues to be spread?"