The images included under-16s in sexualised poses, pages aimed at paedophiles and an image appearing to be taken from a child abuse video.

Among the items not permitted under Facebook's community standards is "sexually suggestive content".

When examples of the images were sent to Facebook to highlight the issue, the company instead reported the journalists who brought them to their attention to police for sharing the pictures.

It subsequently issued a statement: "It is against the law for anyone to distribute images of child exploitation."

Mr Collins said it was extraordinary that journalists had been reported to the authorities when it was trying to "help clean up the network".

Facebook's rules also forbid sex offenders from having accounts but five convicted paedophiles were found to have profiles which it failed to remove when it was brought to their attention, the BBC said.