The prime minister has been working from his flat in No.11 Downing Street since last Friday after testing positive for coronavirus.
In a video message posted on Twitter on Friday, Johnson said: “Although I’m feeling better and I’ve done my seven days of isolation, alas I still have one of the symptoms, a minor symptom – I still have a temperature.
“And so, in accordance with government advice, I must continue my self-isolation until that symptom itself goes.”
Johnson also said it was “crucial” that people continued to obey government orders to stay at home as much as possible.
“A lot of people will be starting to think this is all going on for quite long time and they would rather be getting out there,” he said.
He said while people might be going “stir crazy” they should avoid the “temptation” to break the regulations.
″This country has made a huge effort, a huge sacrifice, done absolutely brilliantly well in delaying the spread of the virus,” he said.
“Let’s stick with it now – remember that incredible clapping again last night for our fantastic NHS. We’re doing it to protect them and to save lives.”
Johnson showed his face in public on Thursday evening when he joined in the nationwide clap for carers at 8pm from the entrance to No.11 Downing Street.
Health secretary Matt Hancock, who has recovered from coronavirus, said today Johnson had been “been working throughout” his isolation.
Hancock said the prime minister was “up and about and on the Zoom conference calls a huge amount, and on the phone”.
The health secretary told Sky News today he had lost half a stone in weight during his own battle with the virus.
On Thursday, he pledged England would hit 100,000 tests a day by the end of the month following widespread criticism of the government’s testing strategy.
But this morning he said the benchmark was only a “goal” rather than a promise.
So far, 163,194 people in the UK have been tested for Covid-19 – roughly 0.2% of the population. Some 2,921 people have died in hospital.