Under the final stage of a plan outlined by Johnson in February, he had hoped to lift most social restrictions on 21 June, meaning pubs, restaurants, nightclubs and other hospitality venues could fully reopen.
That much-anticipated step was pushed back to 19 July.
"I think it is sensible to wait just a little longer," Johnson told a news conference on Monday. "As things stand, and on the evidence that I can see right now. I'm confident that we will not need more than four weeks."