Eleanor Lyons said the measures were fundamentally unfair and could lead to many more victims of slavery and trafficking being denied support. Several women who allege sexual abuse by Fayed said they feared the proposals would undermine investigations into what they describe as his international trafficking network.
Under the legislation, Home Office officials must regard any delay in making a claim of modern slavery or human trafficking as damaging to a claimant's credibility. Any inaccuracy, inconsistency or omission in a person's account, as well as any striking similarity to a claim made by someone else, must also be treated as reasons for disbelief.
Lyons said the credibility tests would harm survivors of sexual violence, who often suffer memory loss as a result of trauma and are reluctant to disclose their exploitation for fear of reprisals by their abusers.
"They are basically saying to victims, if you don't come forward in a timely fashion not yet defined, if there are inconsistencies in your account, and if there are similarities between exploitation and [those of] others, the Home Office decision-maker must question your credibility," she said.
The commissioner said the provisions were particularly concerning for the Al Fayed victims: much time has passed since the alleged abuse, many of the women were exploited in similar ways, and some may not be able to recall exactly when or where events happened because of the impact of trauma.
MPs were told earlier this month that almost half of the women accusing Fayed of abuse are potential trafficking victims.