Children's charities are warning that a number of UK broadband providers are still ignoring government requests to block illegal websites.

The NSPCC and a number of other children's groups are expressing serious concern over the refusal of some UK ISPs to sign up to the Internet Watch Foundation's (IWF) list.

Zen Internet, one of the ISPs that has not implemented the IWF's list, told BBC News: "We have not yet implemented the IWF's recommended system because we have concerns over its effectiveness."

Family-oriented, responsible ISP

The NSPCC's Zoe Hilton said: "Allowing this loophole helps feed the appalling trade in images featuring real children being seriously sexually assaulted."

A Virgin Media spokesperson told TechRadar that: "as a responsible ISP, Virgin Media works within guidelines set by the Home Office and Internet Watch Foundation (IWF) to minimise the availability of content deemed to contain images of child exploitation or abuse."

The Children's Charities Coalition on Internet Safety (CCCIS) wants the government to act to ensure that the remaining ISPs that are not signed up to the IWF's list do so asap.

Call for government action

"700,000 households in the UK can still get uninterrupted and easy access to illegal child abuse image sites," notes the NSPCC's Zoe Hilton.

"We now need decisive action from the government to ensure the ISPs that are still refusing to block this foul material are forced to fall into line. Self-regulation on this issue is obviously failing - and in a seriously damaging way for children."

For more information on the IWF's facilitation of the blocking initiative check out their website. You can also see the full list of ISPs signed up to the initiative on the site.

TechRadar will be speaking to IWF and Home Office reps to get further background on this story, so stay tuned for updates.