It is not illegal to take photographs of naked minors, or every parent in this country would be up on criminal charges. Nor is there a shred of evidence that Bill Henson's models have been in any way abused (they all maintain the opposite). The photographs are not, in fact, taken for purposes of sexual titillation. This is actually unarguable.

Bill Henson has not, in fact, done anything illegal. The fact that you disagree with the fact that he has taken them, even that you find them offensive (though I fail to see how they bear any relationship to child porn) still doesn't make them illegal.