Boris Johnson has been admitted to hospital due to coronavirus after suffering 10 days of symptoms including a high fever, bringing doubts about his capability to lead the response to the pandemic despite No 10 insisting it was purely precautionary.

Johnson was taken to an unnamed London hospital on Sunday after days of persistent symptoms, during which time he has been self-isolating. Last week No 10 had denied 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.

Show more

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.”

Show more

Keir Starmer, the new Labour leader, was among a string of MPs to tweet their best wishes to Johnson. “Wishing the prime minister well and a speedy recovery,” he wrote.

Jeremy Hunt, the former health secretary and Johnson’s main rival for the Conservative leadership last year, tweeted: “Thoughts with Boris Johnson this evening. Whatever political persuasion the whole country is united in wanting our PM to get fit and well as soon as possible.”

Nicola Sturgeon, the Scottish first minister, tweeted: “Wishing the PM all the best and a speedy recovery.”

Donald Trump, the US president, began his Sunday night press briefing by sending well wishes to Johnson.

“He’s a great friend of mine,” Trump said of his British counterpart. “I’m sure he is going to be fine, he’s a strong man, a strong person.”

Johnson’s hospitalisation came after the Department of Health said the number of hospital deaths connected to coronavirus stood at 4,934 people as of 5pm on Saturday, up by 621 from 4,313 the day before.

Among recent fatalities was the first serving midwife confirmed to have died with coronavirus. Princess Alexandra hospital in Harlow, Essex, said Lynsay Coventry, 54, had died on Thursday.

Also on Sunday, scientists warned that the 17.5m antibody home testing kits ordered by the government after Johnson said they could be a “game changer” might fail to detect up to half of coronavirus cases.

It had been suggested the kits would be made available to the public within days, but on Sunday Hancock played down their imminent arrival.

Scientists involved in validating home testing kits told the Guardian that no test on the market has yet been shown to be sufficiently reliable. One expert said they were more likely to detect only 50%-60% of those with milder symptoms.

Also on Sunday:

• Hancock criticised the “unbelievable” behaviour of people packing into parks on a warm day and warned rules on exercise could change, while saying this was not imminent.

• Scotland’s chief medical officer, Catherine Calderwood, resigned after it emerged she twice went to her second home during the lockdown.

• Italy recorded its lowest number of cases in two weeks, with the total number of people in hospital with the virus falling for the first time since the beginning of the crisis.