Marie Stopes International has resumed pregnancy terminations seven weeks after they were suspended because of "serious concerns" about patient safety.
In August, the Care Quality Commission, found poor management and unsatisfactory training before surgery.
Inspectors also questioned arrangements for getting patients' consent for terminations.
Marie Stopes responded by suspending some abortions.
It suspended those undertaken under general anaesthetic or sedation, and all surgical terminations at its centre in Norwich.
It also suspended terminations for vulnerable women and those under 18.
The charity - which provides terminations for 70,000 women every year - was obliged to divert about 250 patients a week to other providers.
In a statement Marie Stopes said it had since made "considerable improvements" in its management structure, adding "we will make sure we learn from this and never again fall below the standards women have every right to expect from us".
It has resumed surgical terminations at its clinic in Brixton in London, and will do so at 12 other centres in England and Northern Ireland by the end of October.
Another 48 clinics carry out medical abortions using drugs alone.
Marie Stopes' voluntary suspension of services followed inspections of its clinics, call centre and corporate headquarters for England by the CQC.
The regulator's deputy chief inspector of hospitals, Prof Edward Baker, said on Friday that he was glad Marie Stopes International's leadership had "accepted the severity of these concerns and taken appropriate action to address them".
Professor Baker said the CQC would continue to monitor the charity as it restarted its termination services.
Concerns have been raised about the decision to allow Marie Stopes to resume all its services before an official report into the failings has been published.
Responding to them, a spokesman for the regulator said "we are satisfied that it has addressed our concerns sufficiently to begin to resume its practice".
"CQC has a duty to ensure that its information and judgements about providers are accurate.
"The inspection reports are still undergoing their checks to guarantee this.
"Detailed reports will be published in due course and will be made available on our website."