These rules are never going to work. Considering that kids will still be able to do a images or video search on Google and come back with tons of smut without needing any age checks shows how ineffective it will be. Kids will always find ways of getting hold of porn. When I was a kid we used to steal magazine and videos from our parents, uncles, older brothers collections and pass them around at school. And once around 12 or 13 we found a load of magazines thrown in the bin around the back of the local shops.
What this new law will probably achieve is to close down some UK based independent sites who will find that their new subscribers numbers drop through the floor after these checks are brought in as customers are put off signing up.