Rt Rev Peter Forster, who's sitting in the House of Lords this week, is worried the proposals don't go far enough.
It's been confirmed age checks will not apply to all online pornography fuelling fears at Westminster that children will still stumble across explicit content.
The verification regime aimed at denying access to under-18s, due to come into force next Easter, will not cover social media sites, such as Twitter, which could host user-generated adult material.
Free sites, where pornography makes up less than a third of overall content, will also be exempt, peers heard.
The House of Lords were debating regulations that will introduce the first system of its kind in the world, requiring commercial pornographic websites to have "robust age verification controls" in place to prevent children accessing explicit material.
But a number of members raised concerns over the limitations of the scheme and the Government has conceded it is "not a complete answer" to the problem.
Speaking in the debate, the bishop said: "My main concern is in relation to access to pornography on websites which don't charge for access.
"Provided their pornographic content is limited to one third of their total content, they are exempted from these regulations."
He said: "What's the rationale for choosing one third and not, say, 10%?
"Parents really don't want their children to stumble across online pornography and arguably children are more likely to stumble across it if it is a website that doesn't charge in the first place."
The bishop added: "I realise that enforcement against every site would be a challenge, but surely the obligation to use access by age verification should be upon all sites which promote pornography.
"What we need is a culture change in relation to child protection, not a partial and piecemeal and limited approach, which I fear these regulations in some respects have."
(Additional reporting from Press Association)
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