Thanks KateMumsnet.
I've looked at TalkTalk's HomeSafe and I don't think it's very good. It only blocks whole websites, it only allows up to 9 exceptions and it's not configurable for different devices or accounts - everybody in the household is subject to the same level of filtering.
This is from the TalkTalk FAQ ...
My children are different ages; can I have separate settings for different ages?
The advantage of these products is that they protect every computer or device in the whole home. As you can change the settings whenever you choose, you should still be able to find the right balance of protection for everyone in your family.
I'm not sure what the 'right balance of protection' would be between a 5-year-old, a teen, a MNer googling dragon butter and a 'D'H who may be a secret or not so secret porn user 
Ideally, something at this 'network level' would be configurable centrally for different devices or accounts. Does anybody know if this is possible? In the meantime, parental controls that are installed on each device (eg K9) are the way to go, IMO.
I am wholeheartedly against any ISP-level filtering because
a) it will be less effective than the device-level parental controls which are currently available
b) it will slow things down for everybody
c) it will be costly and the costs will be passed on to all of us
d) it puts in place a system which could be used by a less benign future government to censor anything they didn't want us to see.
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Focusing more broadly on point 3 ...
To determine what additional tools parents require to protect children from inappropriate content
I think there is currently far too much focus on technological solutions. However good at making filters we get it's only ever going to be a partial solution. We may be able to stem the worst of the tide on our home machines but some inappropriate stuff will always get through. It will do nothing to prevent our DC from accessing content on other devices and networks which are out of our control and it won't stop material being circulated amongst friends.
I see trying to police the internet as a bit like trying to police the street. We can have all the laws we want, lots of police on the beat, traffic calming measures etc. but as well as these, we need to educate our youngsters in the dangers of the street so they can go about in reasonable safety with increasing levels of independence. This starts early - not picking up sweeties off the pavement, how to cross the road, what to do if you encounter a dog you don't know, not going off with strangers - and continues through their teens and into early adulthood - what to do if you're offered drugs, how to handle social drinking, how to get home if you've missed the last bus, what to do if you are mugged ... I think there needs to be a similar emphasis on education when it comes to the internet.
If we don't want our youngsters looking at porn we need to be prepared to talk to them about why in the same way we have conversations about why drugs are a generally bad idea. We need to also have proper conversations with them about illegal downloads, oversharing on FB, online bullying, grooming, gambling, pro-suicide and pro-ana sites, online scams ... a big shiny Porn-Be-Gone! button is no substitute for ongoing supervision, education and guidance.
If there is money to invest in online safety I'd like to see it spent on education and support for parents and young people.
- I'd like to see regular sessions offered for parents - perhaps as part of schools' academic review days/parents evenings - where they can learn about what the dangers are, how to talk to their DC about the issues and how to find, install and use a range of the best filtering tools currently available.
- I'd like to see all aspects of internet safety properly covered as part of the national curriculum. Young people need the space to discuss the issues surrounding internet safety just as they now do around drugs, relationships etc.
- I'd like there to be a named contact in schools who parents or youngsters could go to for help and advice if they encountered any problems with internet safety among their own DC or their friends.
(sorry it was long)