Founded in 1829, Scotland Yard, as the city’s Metropolitan Police Service is known, is the recipient of roughly a quarter of all police spending in England and Wales. (Scotland and Northern Ireland, the other two nations in the United Kingdom, have their own legal systems and police forces.)

The daughter of Oxford academics and a graduate of both Oxford and Cambridge, Ms. Dick was head of counterterrorism at Scotland Yard from 2011 to 2014, overseeing among other things the security operation for the London Olympics in 2012.

She left Scotland Yard in 2014 after 31 years to become general secretary at the foreign office.

Ms. Dick has held command roles in several counterterrorism operations; one operation went terribly wrong in 2005: She was the senior officer in charge when Jean Charles de Menezes, 27, a Brazilian who had been mistakenly identified as an attempted suicide bomber, was fatally shot by officers at a London subway station.

A jury cleared her of any wrongdoing, but Ms. Dick has repeatedly expressed regret. “I think about what happened on that terrible day very, very often,” she said in 2014.

During the search for a new commissioner, the family of Mr. de Menezes wrote a letter to London’s mayor, Sadiq Khan, about Ms. Dick’s potential role. “We have serious concerns about such an appointment and the signal it sends to the people of London,” they wrote.