Boris Johnson bought some breathing space by apologizing for attending a party at his Downing Street office during the first pandemic lockdown, but anger in his ruling U.K. Conservative Party means his grip on power is precarious.

Opposition politicians repeatedly called on him to resign during a heated session of Prime Minister’s Questions in Parliament on Wednesday. By contrast, Tory benches were subdued. It was a sign that Johnson’s apology was just enough to stem the mutinous mood among his MPs.

Following his mea culpa, most Tory MPs interviewed by Bloomberg said they would now wait for the findings of a formal probe into the pandemic rule-breaking party — and other Downing Street gatherings — before deciding on any next steps. It would take 54 of them, or 15% of the total, to trigger a vote on Johnson’s future.