LONDON — Hundreds of officers and other employees of the police in Britain have used their power to sexually abuse vulnerable people, a report released on Thursday by a national watchdog said, the latest in a string of institutional abuse accusations in the country.

Among those targeted, in what the independent agency called “the most serious corruption issue facing the service,” were victims of domestic abuse, drug and alcohol addicts, and people who work in the sex industry, some of whom were in custody at the time.

The inquiry by Her Majesty’s Inspectorate of Constabulary, which assesses national police forces, found that there had been 436 accusations of sexual abuse by police officers in England and Wales over the two years through the end of March. It said the accusations involved 334 police employees, including 306 officers. The watchdog also emphasized that the scale of the problem was much larger.

The leader of the inquiry, Mike Cunningham, a former chief constable of the Staffordshire police in central England, said the abuse was an egregious breach of officers’ roles as guardians and protectors.