Internet service providers in Ireland are refusing to blacklist access to known child pornography websites, citing concerns about the possible legal ramifications, costs and the effectiveness of such a move, the Sunday Tribune has learned.

In a revelation that has prompted strong criticism by the children's charity Barnardos, it has emerged that images of child sexual abuse which are reported to the hotline.ie website, operated by the Internet Service Providers Association of Ireland (ISPAI), are not automatically blocked.

Instead, the ISPAI reports such content to authorities in the countries where they are operating from, with a view to having it removed and the individuals behind it prosecuted.

It acknowledges that although this can happen within 24 hours, on other occasions it proves impossible.

As a result, this means it can still be accessed by Irish internet users, despite having been reported to the ISPAI. Although a blacklist of such websites is in operation in Britain, ISPAI general manager Paul Durrant said the technology necessary to accurately block such content is not sufficiently developed.

"At present in Ireland there is no blacklist, and I will tell you why. It's because a blacklist is totally ineffective and this material is moving so quickly… I would say the best thing is to actually get it removed," he said.

He said ISPs in Ireland also had to consider the possible legal implications associated with importing such a list to Ireland, and said it may be necessary to indemnify them against inadvertently doing "collateral damage" to a website which may innocently end up on such a list. He added that maintaining the security of the blacklist would also pose a challenge.

"At the end of the day, telecommunications companies have to make a profit … when you weigh that up against the lack of effectiveness, you have to ask is this the best way?" he said.

But the chief executive of Barnardos, Fergus Finlay, strongly criticised the failure to block access to such material in Ireland.

He said the market for child sexual abuse imagery "is huge" and that it is "one of the key risks" to children.

"Of course, efforts have to be made to apprehend perpetrators, but perpetrators exist because there is a market," he added.