Multiple newspapers learned on Friday that the Prime Minister would take the drastic step of plunging England into another national lockdown this week to stem the second wave of coronavirus.
The Times reported that he would hold a press conference on Monday after discussing alarming new data with Chancellor Rishi Sunak, Cabinet Office minister Michael Gove and Health Secretary Matt Hancock.
But No 10 hastily arranged a press conference for Saturday after the information became public, amid outrage that newspapers should learn of the new measures through leaks or official selective briefings.
In a move to placate their anger, Mr Johnson sent a message to Conservative MPs on WhatsApp to apologise and warn there are "no easy short term options".
"Folks - so sorry that you've had to hear about all this from the newspapers today," he wrote in a message seen by the PA news agency.
"Let me assure you that the leak was not a no10 briefing and indeed we have launched an inquiry to catch the culprit. I had hoped to make the announcement in Parliament on Monday but to avoid any further uncertainty I'll now do a press conference from Downing Street this evening.
"My team will make sure you have access to all the data and briefing from scientists you need in the coming days. Please speak to your whip if you have anything to feed in.
"I assure you we are doing what we believe is best for the country and to ensure that the NHS is not overwhelmed in a way that could cost many thousands of lives.
"There is a clear way out of this, with better medication and rapid testing - and the genuine prospect of a vaccine. Our country will recover well. But I am afraid there are no easy short term options. Best Boris."