As with all filters...
...take theirs with a grain of salt. Filters are unreliable at best. Child porn sites and other 'undesirables' on the internet often change IP addresses and host providers, some of them daily. Most are not even publicly published nor advertised, requiring invitations via instant message, email, etc to even get a site IP address to go to.
If any single entity would have a 'reliable' list, it would be Google from what the Googlebot crawls on a daily basis. As we all know, those SE bots crawl everything, even with robots.txt defined (that just prevents them from indexing the material, btw). Any list with manually entered addresses fail, and fail hard.
Oh, and for you folks there across the pond, this J. Smith person sounds like a right twat. Why don't you do yourselves a favor and vote her out on her ass next election. For someone like her to get in, it's almost like she Gerrymandered her votes or something.
Also, that agency someone mentioned above that REALLY is doing the work of saving abused children and arresting predators...that group you should all donate funds to or send them mail thanking them in support for their efforts. It wouldn't hurt to write editorials for your local papers either in support of the work they do. Those types of agencies are what we need more of, not the do-nothing types like the IWF (or frankly most of the US Congress and related governmental agencies).
No icon because there is nothing appropriate to choose from ( I suggest a pic of J. Smith dressed as the Wicked Witch of the West be added).