The apology comes at a particularly unwelcome time for the C.I.A. as the Trump administration’s nominee to lead the agency, Gina Haspel, has been under intense scrutiny this week over her role at a secret detention site in Thailand, the same country where the Libyan couple was once held.
Mr. Belhaj, who is now a politician in Libya, criticized the nomination of Ms. Haspel, who in 2002 oversaw a C.I.A. “black site” in Thailand that, he said, sounded like the one where he was held.
“What does it mean for someone to be elevated and honored, someone who oversaw a secret prison in Thailand where torture was being practiced?” he said.
In an article for The New York Times this week, Ms. Boudchar described her time in C.I.A. captivity in Thailand. She said black-clad figures wearing ski masks trussed her, chained her to a wall and assaulted her. “They hit me in the abdomen just where the baby was,” she wrote. “To move me, they bound me to a stretcher from head to toe, like a mummy. I was sure I would shortly be killed.”
After her transfer to Libya, Ms. Boudchar said, she was held in a filthy prison and released just before she gave birth. Her newborn son weighed just four pounds, which she attributed to her mistreatment at the hands of the C.I.A.
On Thursday, Ms. Boudchar, wearing a head scarf and dark glasses, emerged with her son, who is now 14, from Parliament holding aloft her copy of the apology letter. “The British government has apologized after six years,” she said through an interpreter.
Mr. Allen and Britain’s former foreign secretary, Jack Straw, were both named in the original lawsuit but were withdrawn by agreement in May. Under a settlement, Britain has not admitted any liability, but Mrs. May said the government had “learned many lessons from this period.”
“We should have understood much sooner the unacceptable practices of some of our international partners,” she wrote in her letter.