People in England will be banned from socialising in groups of more than six from Monday following a sharp rise in coronavirus infections, with almost 3,000 new cases confirmed every day this week.
Boris Johnson said the Government had been forced to act because some people had failed to follow social distancing guidelines.
Watch: Yahoo UK’s News Editor, Chris Parsons explain what a local lockdown is
But a Cabinet source told the MailOnline the new rule was objected to by every member of Mr Johnson's coronavirus strategy committee on Tuesday apart from the Health Secretary.
"Everyone apart from Hancock wanted to set the limit on groups at eight or more," the source said.
"Even the PM was initially cautious about taking the limit all the way down to six.
"The majority view was that this level of social distancing will have a huge impact on people's lives and the economy. But Hancock got his way."
The Health Secretary is said to have driven the decision, backed by Chief Medical Officer Chris Whitty and Chief Scientific Adviser Sir Patrick Vallance.
Those in attendance on Tuesday included the Prime Minister, Rishi Sunak, Dominic Raab, Michael Gove, Mr Hancock, Alok Sharma, Priti Patel, and Grant Shapps.
Speaking about the disagreement among ministers, a source told the Mail: "I wouldn't characterise it as a row, but it's fair to say there was a vigorous debate."
But Downing Street denied Mr Johnson was steered into the rule of six decision by Mr Hancock.
"The PM wasn't talked round by anyone," an insider told the Mail.
A source close to Mr Sharma played down reports he opposed the rule of six, telling the publication he accepted the decision. Treasury sources also said Mr Sunak supported the restriction.
The rules will apply across England to all ages and to indoor and outdoor gatherings, including private homes, parks, pubs and restaurants.
There will be a few scenarios where the restrictions do not apply, such as if the household or support bubble is larger than six people, or if people are gathering in a large group for the sake of work or education.
Weddings, funerals and organised team sports will also be exempt if they are conducted in a Covid-secure way.
Mr Johnson said the Government had been forced to act because some people had failed to follow social distancing guidelines.
"With the best will in the world people have not, I’m afraid, been totally following the guidelines," he told a Downing Street press conference.
"I certainly don’t want to blame people but now is the time for us to focus, to concentrate and to enforce the rule of six."
Mr Johnson added that the new rules were being introduced to "prevent another wholesale national lockdown".
Striking an optimistic note, he said he is “still hopeful” that “we could be able to get some aspects of our lives back to normal by Christmas”.