“Taking into account the missing records,” the report said, “there were probably at least another 200 patients similarly affected but whose clinical notes were not found.”

The patients were often given heroin through a syringe driver, also called an infusion pump, a device that can deliver a steady supply of medication, usually intravenously, over a long period of time. Many were given opioids not only unnecessarily and in dangerous dosages, but in dangerous combinations with sedatives.

A large number of cases involved one doctor, Jane Barton, who the report said had established a pattern that was followed by others. A disciplinary panel investigating a small number of those cases censured Dr. Barton in 2009, and although she retired, she was not prohibited from practicing medicine.

Dr. Barton did not speak to the news media on Wednesday. It was not clear whether the authorities would pursue criminal charges against her, as some families of her patients have demanded.

Nurses began to complain about the inappropriate use of heroin in the hospital in 1991, but administrators consistently overrode their concerns, the report said. Family members began to object a few years later, and fought for years to be heard. A series of investigations that followed were either limited in scope or largely ignored.

If people had listened to the relatives and nurses, “many of those deaths would not have happened,” Jeremy Hunt, the health secretary, said in Parliament, apologizing on behalf of the government.

One nurse at the hospital, Pauline Spilka, told investigators that despite her experience in elderly care, she had never heard of a syringe driver before working at the War Memorial Hospital. She learned later that it was a device that delivers a constant dosage of pain relief for seriously ill patients.