Latest Department for Transport figures show that vehicle use increased on Monday.
By Sunday, use of motor vehicles had fallen by 73 per cent compared with February 27.
But a spike in traffic led to Monday’s figure showing just a 63 per cent decline compared with the same date.
This was the first daily rise in two weeks.
Professor Yvonne Doyle, director of health protection for Public Health England, said: “This shows a slightly concerning trend, because we have seen an uptick in motor vehicle traffic.
“The message here is really people do need to stay at home.
“Most are doing the right thing, as you can see from the rapid decline in public transport use.
“Everyone needs to do that.
“The message here is we need to save lives and protect the NHS, so please stay at home.”
Speaking at the daily press briefing in Downing Street Prof Doyle also said the number of hospital admissions from the virus, which rose for the third day running, was a worry.
She said: “It is slightly concerning.
“It’s still too early to say whether the plateau of hospital admissions has ended but we’ve now seen three days of increases in a row and again, we need to protect the NHS, and the best way to do that is to stay at home, to avoid catching the disease yourself and obviously avoid giving it to anyone else.”
On hospital admissions, she said London “is where coronavirus is most advanced”, adding: “But the chart shows that the threat is everywhere, we need to protect the NHS everywhere and the Midlands now is obviously a concern as well.”
Comparing the UK to other countries, Prof Doyle added: “As things stand it has not been as severe here as in France and we’re just tucked in under the USA and obviously Italy on a different trajectory, but… and Spain and the United States, as we’ve said.
“But there’s no reason to be complacent.”
She said there is currently capacity for around 3,000 tests for frontline NHS staff, which will increase.
Asked how many frontline workers are being tested, she said: “The number of tests undertaken in the NHS and Public Health England combined testing capacity is just increasing at the moment.
“So that will be a relatively small number but there is capacity, for example, today for almost 3,000 and that will increase as we get to 25,000, that capacity.
“But the important capacity is in the second strand where we have five centres where people can drive through and get their testing done in order of priority.
“NHS chief executives are identifying that priority and the intention here is to get from thousands to hundreds of thousands within the coming weeks.
“So we are very committed to our NHS frontline staff.”