For Britain’s prime minister, Theresa May, the good news is that she still has her job, almost three months after she lost her parliamentary majority in a botched general election she need not have called.

The not so good news is that her declaration that she intends to remain prime minister into the next decade was novel enough to make front-page headlines.

Speaking late Wednesday on a trip to Japan, Mrs. May surprised some members of her Conservative Party by suggesting that she wants to stay on indefinitely as prime minister, perhaps even leading the party into the next general election, scheduled for 2022.

Echoing some of the steely language of Margaret Thatcher, Britain’s first female prime minister, Mrs. May said she was “not a quitter,” and dismissed reports that she would step aside in 2019, after her country’s planned withdrawal from the European Union.