842,355 English and Welsh Lunatics

Ancestry now has online registers kept by the Lunacy Commission, 1846 to 1913, of asylum patients in both public and private asylums. They record the name and sex of the patient; the name of hospital, asylum, or licensed house; and the date of admission and of discharge or death of each patient.
Annual admissions recorded in the register increase from about 6,000 at the start of the record to over 20,000 at the end.
The original data source is Commissioners in Lunacy, 1845–1913. Lunacy Patients Admission Registers, Series MH 94. The National Archives, Kew, England.

Two smaller related collections sourced from TNA also debut on Ancestry:

4,332 records: England & Wales, Criminal Lunacy Warrant and Entry Books, 1882-1898
613 records: England, Criminal Lunatic Asylum Registers, 1820-1843