London may face a coronavirus lockdown similar to those seen in other European cities, as Boris Johnson warned the country he was prepared to take “further and faster measures” to tackle the disease.

While Downing Street is understood not to be planning to impose more stringent measures immediately, the prime minister said he would not hesitate to roll out tougher action to protect people’s health and NHS services when necessary, as officials reiterated the capital was ahead of other parts of the country in terms of the virus’ spread.

In his daily press conference, Johnson said: “We’ve always said we’re going to do the right measures at the right time.

“I think a lot of people are making a real heroic effort to comply with the advice that we have given but as I’ve said tonight and in the past few days we keep everything under continuous review and we will not hesitate to bring forward further and faster measures where we think that is necessary.”

It emerged on Wednesday that the Cabinet Office had written to Whitehall departments asking for their recommendations on stricter measures for the capital, in a “shielding plan for London”, where 953 people have been diagnosed with Covid-19 – nearly a third of the 2,626 UK total.

Johnson ended his briefing by repeating his warning that more stringent measures were still on the table. He said: “Absolutely we do not rule out … because it would be quite wrong to do so … we do not rule out taking further and faster measures in due course.”

His remarks came as Scotland’s first minister, Nicola Sturgeon, suggested the government was considering a far tougher strategy to deal with the coronavirus.

She attends the government’s regular emergency Cobra meetings and said she expected the UK government to announce “more stringent measures” for the capital, where the disease is spreading at a faster rate than the rest of the country.

Asked if he would introduce legislation to specifically reduce people’s movements, Johnson said it was not a natural choice for a government that valued liberty, but he ruled nothing out when the pandemic reached its peak.

One source with close knowledge of the capital’s response to the outbreak said any plans were not imminent and had not been discussed with key organisations who would have to be involved, such as the Metropolitan police, City Hall and those handling London’s response.

London has the highest level of infection and that rate is being monitored daily. The government is also getting daily figures on transport use in the capital. The Guardian understands the latest figures show a sharp drop, since the government urged people to stay home on Monday, with use of the tube network down almost 50% on its normal level and bus use down almost 40%.

In some European countries including Italy and France, people have been restricted to their houses and face a fine if they leave for any reason other than to buy food, visit the pharmacy or go to their job if they cannot work from home.

The British government has come under criticism for its failure to bring in mandatory social distancing measures to slow the spread of the virus, with Johnson saying on Monday only that people should avoid “non-essential contact”.

One source at City Hall said there had been no word of immediate action from No 10 on moving to far more strict measures on people’s movement.

“We’ve not been told anything at all about this yet, which would indicate there’s nothing due immediately. But we are ready to take what action is needed to protect the health of Londoners,” the source said.

Other sources said that with London confirmed as being more advanced than the rest of the UK in the spread of the disease, the general expectation was that new containment measures would be rolled out in the capital first.

Asked about the possibility of a lockdown for London, the prime minister’s official spokesman said the measures to protect people from coronavirus would be guided by scientific advice.

Quick guide What to do if you have coronavirus symptoms in the UK Show Hide Symptoms are defined by the NHS as either: a high temperature - you feel hot to touch on your chest or back

a new continuous cough - this means you've started coughing repeatedly NHS advice is that anyone with symptoms should stay at home for at least 7 days.

If you live with other people, they should stay at home for at least 14 days, to avoid spreading the infection outside the home. After 14 days, anyone you live with who does not have symptoms can return to their normal routine. But, if anyone in your home gets symptoms, they should stay at home for 7 days from the day their symptoms start. Even if it means they're at home for longer than 14 days. If you live with someone who is 70 or over, has a long-term condition, is pregnant or has a weakened immune system, try to find somewhere else for them to stay for 14 days. If you have to stay at home together, try to keep away from each other as much as possible. After 7 days, if you no longer have a high temperature you can return to your normal routine. If you still have a high temperature, stay at home until your temperature returns to normal. If you still have a cough after 7 days, but your temperature is normal, you do not need to continue staying at home. A cough can last for several weeks after the infection has gone.

Staying at home means you should: not go to work, school or public areas

not use public transport or taxis

not have visitors, such as friends and family, in your home

not go out to buy food or collect medicine – order them by phone or online, or ask someone else to drop them off at your home You can use your garden, if you have one. You can also leave the house to exercise – but stay at least 2 metres away from other people. If you have symptoms of coronavirus, use the NHS 111 coronavirus service to find out what to do. Source: NHS England on 23 March 2020

Johnson said earlier this week that London was moving ahead of the rest of the UK on the curve of the coronavirus’s spread and people should heed the advice on social contact.

Powers under the 1984 Public Health (Control of Disease) Act could be deployed in a lockdown scenario. It allows for individuals “to be kept in isolation for their own safety”, the prime minister’s spokesman said.

The government is already expected to introduce emergency powers to shut premises, restrict gatherings and scale back transport services.

On Wednesday evening Transport for London announced it would run a reduced service “to enable London’s critical workers to make essential journeys”.

The Waterloo and City line will be suspended from Friday in response to declining demand and staff availability.

And the night tube, London Underground’s 24-hour weekend service, is to be closed with immediate effect. The service operates on Friday and Saturday nights on the Northern, Central and Victoria lines, as well as parts of the London Overground.

The move will help restrict non-essential travel to bars and restaurants, as the prime minister contemplates a crackdown. It also comes among increased staff anger at the risk of working on tube lines at night to serve passengers ignoring public health advice to avoid gatherings.

The Mayor of London, Sadiq Khan, urged Londoners to only use public transport for essential journeys, he said: “People should not be travelling, by any means, unless they really, really have to. Londoners should be avoiding social interaction unless absolutely necessary, and that means they should be avoiding using the transport network unless absolutely necessary … ensuring the capital’s critical workers can move around the city will be crucial.”