Staff at Marie Stopes International (MSI) had "limited training" in resuscitation and clinicians were found to be "bulk-signing" forms authorising abortions, the Care Quality Commission (CQC) said.
In a report, the provider was accused of putting women at risk by failing to adequately train staff and neglecting to obtain proper consent from patients.
The family planning provider suspended surgical abortions for girls under 18 and vulnerable women in August after concerns were raised by the CQC about patient safety.
It also halted terminations under general anaesthetic or conscious sedation and suspended all surgical terminations at the provider's Norwich centre.
But the organisation, which performs around 70,000 abortions every year, was allowed to resume services in October after satisfying the CQC that it had improved standards.
On Premier's News Hour, Peter D Williams, Executive Officer at Right to Life, said the report left him "quite horrified".
"This is actually worse than I thought it was going to be," he said, "This is quite a damning indictment of the failures and abuses of Marie Stopes International".
Marie Stopes said it had "made considerable changes to our management, governance and assurance processes" but, despite that, the Care Quality Commission warned it would "continue to monitor its services very closely".
Williams told Premier this did "not entirely" reassure him.
"It doesn't assure me that Marie Stopes staff are truly going to reform their organisation to make sure that these safety issues are resolved," he added.
Suzanne Ash, interim managing director at Marie Stopes UK, said: "Since the inspections, we've made considerable changes to our management, governance and assurance processes, including extensive training of staff, and updating of policies.
"We have learned from this, and intend to continue our focus on providing the safe and compassionate care that women expect and deserve."
Peter D Williams speaking to Premier's Alex Williams: