Boris Johnson deliberately misled British lawmakers over lockdown-breaking parties in Downing Street during the coronavirus pandemic, a powerful committee concluded on Thursday, releasing publicly the findings that prompted Mr. Johnson’s angry resignation from Parliament last week.

The 108-page document, produced by the House of Commons privileges committee, offered a damning verdict on Mr. Johnson’s honesty and integrity, concluding that his conduct in misleading lawmakers who questioned him, including about his publicly documented violations of lockdown policy, was deliberate and that he had committed “a serious contempt” of the House.

“The contempt was all the more serious because it was committed by the prime minister, the most senior member of the government,” the report concluded. “There is no precedent for a prime minister having been found to have deliberately misled the House.” In addition, it said, “He misled the House on an issue of the greatest importance to the House and to the public, and did so repeatedly.”

Had he remained a lawmaker, the punishment recommended by the committee would have been a 90-day ban from Parliament, one of the most severe options it could have suggested. The report also recommended that the former prime minister’s parliamentary pass should be revoked, preventing him from visiting Parliament as he would normally be entitled to do.