The Home Office and the Association of Chief Police Officers (ACPO) has launched a public reporting webpage (on the Directgov website) for terrorist-related material found on the internet.
The public can report URLs of suspected terrorist material direct to a police unit who will investigate. If the website is found to be in breach of the Terrorism Act 2006 the police will issue a Section 3 Notice to have the content modified or removed presuming it is hosted in the UK.
The type of content users may report can be found here on the Home Office website and the reporting page itself here.
As part of the fight against terrorism this must be good though I imagine it will be difficult to maintain an adequate level of publicity for the scheme so that people know where to look to report a website.
Also the savvy terrorist will use hosting provider in a country that doesn’t care or doesn’t have the same laws so unless this initiative was conducted on a global scale it will probably only have a small effect.