Foreign Secretary Dominic Raab said it was "not sustainable" to keep the lockdown in place "permanently" but that the Government was monitoring the changes it was making.

Speaking at the daily Downing Street coronavirus briefing, Mr Raab said: "It is true to say that making any changes inherently comes with some risk of spreading the virus compared with simply staying at home.

"But it is also true that staying in permanent lockdown is itself not sustainable on health grounds or economic grounds.

"That is why we have only eased measures where it can be done with the lowest risk possible.

"That's also why we are watching the impact of every change we make very closely."

Deputy chief medical officer for England Professor Jonathan Van-Tam said evidence from Apple Maps searches suggests only a "gradual" increase in walking and driving while public transport use has not risen.

He told the Downing Street briefing: "You can see that there's been a gradual, but only gradual, upward trend in searches related to walking and driving but for public transport this trend is essentially flat.

"This is very much in line with the guidance that the Government has issued about avoiding public transport wherever possible, saving it for key workers, and clearly this is a trend that the public are following."

Prof Jonathan Van-Tam said very few Covid-19 patients experience loss of taste and smell as a lone symptom of the virus.

Asked whether the UK had missed diagnosis of coronavirus by failing to add it to the list of symptoms to watch for until this week, the deputy chief medical officer said: "What I can tell you is from the Public Health England data set, called the FF100 - the first few hundred cases - there are actually 229 cases in there, all laboratory-confirmed Covid, all of whom have been studied in considerable detail and 0.44% reported anosmia on its own as a symptom.

"So, the point about anosmia is it doesn't always come as the first symptom.

"Even if it does, it is followed by the cough, the fever and many of the other symptoms I have talked about, referring to the WHO definition.

"So you don't miss those cases.

"The important thing was to work out if this would add any sensitivity to the diagnostic cluster we were using and the answer is that it makes a small - a very small - difference and we have therefore decided to do it."

England's deputy chief medical officer Professor Jonathan Van-Tam said the country had to prepare in case Covid-19 came back in the autumn and winter.

Only once there was a vaccine that is "really capable of suppressing disease levels" will the country be "out of this".

"So from that perspective we may have to live, and learn to live, with this virus in the long-term, certainly for many months to come if not several years," he said.

He said more information was needed on the seasonality of Covid-19.

"One of the things that's very clear with flu viruses is that they come in our cold winters and the levels of transmission and circulation decline over the summer months.

"The data we have on other coronaviruses we have looked at very carefully, and it's not clear that these coronaviruses are as seasonal as influenza.

"But there may be an element of seasonality and it may well be that the autumn and winter conditions provide a better environment for the virus to then do its work again."

Foreign Secretary Dominic Raab defended the Government's record on testing and the app development.

"We are learning all the way as we go through this pandemic, not just on the scientific side but on the innovation that we need to get a grip on it," he said at the Downing Street briefing.

"We are making good progress on the testing and on the tracing and on the pilot in the Isle of Wight in relation to the app."

Prof Van-Tam said that it "does not seem" that children are "high-output transmitters" of coronavirus like they are with the flu.

He said that most children have only "extremely mild" Covid-19 symptoms and the infection rate among them is "about the same" as in adults, but "possibly a little lower" in younger aged children.

Prof Van-Tam said the "data are pretty sparse at the moment" with regards to children's ability to transmit the virus to adults.

"But the experts have already had a look at this and formed a conclusion that unlike influenza, unlike flu, where we are very clear that children drive transmission in the community to adults, it really does not seem to be the same kind of signal with Covid-19, that children are not these kind of big high output transmitters as they are with flu," he added.

Quizzed on whether the UK would support an international investigation into coronavirus' origins and China's role in it - as pushed for by Australia - Mr Raab said: "Certainly, at the international level, we have been clear - and we work with all of our partners, including Australia and many others - because we want this review to command the strongest support because it is more likely to be effective if it does.

"Obviously it is going to be international, it has got to be credible, which means it is independent and impartial, and it has got to be able to get to the bottom of how it (the virus) happened, how the outbreak happened and spread and, critically, the lessons we can learn for future pandemics."