The day after the crash, the United States Embassy in London told the Foreign Office that the wife of an air force base employee had been involved in a traffic accident, Mr. Raab told the House of Commons on Monday.

On the same day, the police applied to waive Ms. Sacoolas’s immunity in the case, Mr. Adderley said.

And despite an assertion by Washington that she was covered by immunity, Britain made a formal request to the United States Embassy on Sept. 5 to waive that protection.

That request was declined, and on Sept. 13 the embassy informed the British authorities that Ms. Sacoolas “would be leaving the country imminently, unless the U.K. had strong objections,” Mr. Raab said on Monday — the first public acknowledgment that the British government had been warned of Ms. Sacoolas’s impending departure.

Mr. Raab said that the government had “duly and immediately objected in clear and strong terms.” Even so, Ms. Sacoolas left Britain on Sept. 15. According to Mr. Raab, the Foreign Office was informed of her exit the next day.

Officials notified the police, Mr. Raab said, but asked them not to tell Mr. Dunn’s family for a day or two in order to give the government time to decide on a course of action.