A man convicted of child abuse is fighting a court ruling that his victim should not be forced to pay his $20,000 legal bill.

Mark Wurth was repeatedly sexually abused by his geography teacher and housemaster, Neville Gilbert Betteridge, at the Blue Mountains Grammar School in the 1970s.

In 2004, Betteridge was convicted of indecently assaulting Mr Wurth and given a three-year suspended jail term.

Seven years later, Mr Wurth sued Betteridge and the Anglican Church, which ran the school, for damages and the church paid him an out-of-court settlement.

But when he tried to withdraw his claim against Betteridge, his abuser demanded he first pay his $20,000 legal bill.

"I was just, you're joking? You know? Like when does a victim pay a perpetrator's costs?" Mr Wurth said.

"I was shattered and depressed, and then the more I thought about it, it made me more despondent with the legal system that they can be allowed to do this.

Got a confidential news tip? Email ABC Investigations at investigations@abc.net.au For more sensitive information: Text message using the Signal phone app +61 436 369 072 No system is 100 per cent secure, but the Signal app uses end-to-end encryption and can protect your identity. Please read the terms and conditions.

"It's very similar to how I felt when he was abusing me as a kid.

"I have no control. I'm just made to do what he says. There's nothing I can do."

In July, a Supreme Court judge ruled that any attempt by Betteridge to pursue his victim would be a "conspicuous waste of emotional and financial resources" and made no order as to costs.

But Betteridge is now seeking leave to appeal that decision, arguing the judge considered irrelevant matters and made manifest mistakes.

Church calls on abuser to drop the claim

The Anglican Church has called on Betteridge to drop the claim, but his barrister, Paul Glissan, told the ABC he was entitled to seek costs under court rules.

New South Wales Greens MP David Shoebridge said while the appeal was legal, it was morally questionable.

Mark Wurth said he was shocked when his abuser demanded he pay his legal bill.

"When you take one step and have a look at what this man's been through, he's already been the subject of appalling sexual abuse and what's happening to him now in the legal system has all the hallmarks of secondary abuse," Mr Shoebridge said.

"This is a man who should be getting support from the legal system, not facing these endless appeals."

Mr Shoebridge said the case highlighted the need for law reform to better protect victims of child sexual abuse.

"The core problem that this case demonstrates is there is no simple, straightforward remedy for the victims of child sexual abuse," he said.

"Whether it is against the Catholic Church, where there's byzantine trust structures that defend church property, or here where it is against part of the Anglican Church, and it's the failure to be able to identify a very clear legal entity to sue.

"There must be a clear path to compensation."

The application seeking leave to appeal will be heard early next month.