LONDON — Britain is giving up its efforts to strike a deal with the uncompromising European Union and will not return to the table. It will seek to leave the European Union, even without a deal. And toward that end, it will sabotage the bloc, sending provocateurs to represent it in Brussels and penalizing countries that vote to grant another Brexit extension.

So went the drumbeat of recrimination from officials, mostly anonymous, inside 10 Downing Street, as Prime Minister Boris Johnson’s already dim hopes for a negotiated exit with Brussels appeared to flicker out on Tuesday.

The threats and warnings from London are meant to disguise a highly inconvenient truth: Mr. Johnson is legally obliged to ask the European Union to extend the deadline of Oct. 31 for its departure from Europe, if he does not reach a deal by Oct. 19, despite his vow never to do so.

As the prime minister girds for a likely election, his political survival depends in part on looking like he is being dragged, kicking and screaming, into this reversal. Everything Mr. Johnson says and does is calculated to advance the narrative that he has been forced — by an irresponsible Parliament, overreaching courts and truculent Europeans — into breaking his promise.