Australian human rights lawyer Geoffrey Robertson says Pope Benedict's resignation could expose him to lawsuits from victims of pedophile priests.

Robertson, writing in UK newspaper the Independent, argues the Pope's resignation is "merely expedient" as he'd become too old to cope in the job.

"It would have been both astonishing and courageous, a few years ago, had it been offered in atonement for the atrocity to which he had for 30 years turned a blind eye - the rape, buggery and molestation of tens of thousands of small boys in priestly care," writes the author of The Case of The Pope: Vatican Accountability for Human Rights Abuse.

Robertson, based in London, argues the Pope's "command responsibility" goes back to 1981 when he was appointed head of the Vatican body that disciplines errant priests.

Letters from then Cardinal Ratzinger have emerged in US court cases "always protective of rapist priests", he writes.

Robertson notes as a head of state Pope Benedict has absolute immunity from legal action, but that won't remain when he retires.

"There are many victims of priests permitted by Cardinal Ratzinger to stay in holy orders after their propensity to molest was known and they would like to sue the ex-Pope for damages for negligence," the lawyer states.

"If he steps outside the Vatican a court may rule that they have a case."