Boris Johnson, British Prime Minister, has been admitted to hospital due to coronavirus after suffering 10 days of symptoms including a high fever.

Boris Johnson was taken to an unnamed London hospital on Sunday after days of persistent symptoms, during which time he has been self-isolating.

This issue has brought about doubts about his capability to lead the response to the pandemic despite No 10 insisting it was purely precautionary, denying that the prime minister was more seriously ill than claimed.

A Downing Street spokesperson said: “On the advice of his doctor, the prime minister has tonight been admitted to hospital for tests. This is a precautionary step, as the prime minister continues to have persistent symptoms of coronavirus 10 days after testing positive for the virus.”

The spokesperson said Johnson would stay in hospital “as long as needed”.

Officials were keen to stress that this was not an emergency admission, and that Johnson will remain in charge of government, and will be in regular touch with colleagues and civil servants.

A government source told Reuters on Monday morning that Johnson had spent the night in hospital.

If his condition worsens, Dominic Raab, the foreign secretary and first secretary of state, is the designated minister to take charge.

Raab is expected to chair a 9.15am Monday meeting of the government’s C-19 committee, which leads the response to the pandemic.

The pound fell against the dollar and euro overnight on Monday as foreign exchange markets took fright at the possibility of Johnson being out of action.

Boris Johnson had been hoping to leave quarantine on Friday but his persistent temperature meant he had to remain inside his flat at No 11 Downing Street.

The Guardian was told last week that Johnson was more seriously ill than either he or his officials were prepared to admit, and that he was being seen by doctors who were concerned about his breathing.

But Downing Street flatly denied that the prime minister’s health had seriously deteriorated, and insisted there were no plans at that point for him to be admitted to hospital.

Earlier on Sunday, Matt Hancock was asked just how ill the prime minister was. The health secretary told Sophy Ridge on Sunday: “He’s OK. I’ve been talking to him every day, several times a day … he’s very much got his hand on the tiller. But he’s still got a temperature.” He added: “He’s working away inside Downing Street. He’s in good spirits.”

Hancock himself has only recently come out of isolation after testing positive for coronavirus, although his symptoms appear to have been notably milder.

Johnson’s partner, Carrie Symonds, who is pregnant, revealed on Saturday that she had also been suffering from the virus but is recovering.

While No 10 did not say what tests Johnson would undergo in hospital, experts said they would be likely to focus on assessing how the prime minister’s lungs, heart and other organs were responding to the virus.

“Doctors will be monitoring important vital signs such as oxygen saturations,” said Dr Rupert Beale, who heads the cell biology of infection laboratory at the Francis Crick Institute in London.

“They will also check blood tests to see what the immune response to the virus looks like, and to assess liver and kidney function. They will perform an electrocardiogram to check the heart. More sophisticated tests may include a CT scan of the chest to get an accurate picture of the lungs.”