The Prime Minister has warned against drawing “premature conclusions” about dropping coronavirus cases as a leading expert said the worst of the pandemic could be behind us by late September.

Boris Johnson told reporters that the easing of restrictions on July 19 across England had not yet shown up in the figures.

Speaking during a visit to Surrey Police HQ in Guildford, he said: “I’ve noticed, obviously, that we are six days in to some better figures.

“But it is very, very important that we don’t allow ourselves to run away with premature conclusions about this.

“Step four of the opening-up only took place a few days ago, people have got to remain very cautious and that remains the approach of the Government.”

Mr Johnson acknowledged people’s frustrations about the self-isolation system but insisted they had to “stick with the programme”.

The Prime Minister, on his first visit since being released from self-isolation, said: “I know that people have been frustrated about the pinging and the self-isolation.

“I totally understand that, particularly now as we’re starting to see some better figures.

“But I think everybody understands that this is still a very dangerous disease.

“We do need to use the tools that we have.

“Self-isolation is the one that we’ve got.

“I urge people to do it.”

The new test-to-release system would come in on August 16 but “until then, please could everybody stick with the programme”, he said.

I’m positive that by late September or October time we will be looking back at most of the pandemic

Asked whether students would need to be fully vaccinated to attend lectures and football fans double-jabbed to go to matches, Mr Johnson said the “young people of this country are doing an incredible job of coming forward to get vaccinations”.

He added: “The figures are outstanding.

“It’s almost 70% now of 18-20 year-olds who have come forward to get jabs, it’s just wonderful.

“It is a great thing to do.

“I would just say that my message to everybody is: get your first jab if you haven’t yet got one, but get your second jab too.

“It will help protect you, protect your family and help us all to move forward.”

Earlier, Professor Neil Ferguson, whose modelling was instrumental to the UK going into lockdown in March 2020, said it will be “several more weeks” before the effect of the July 19 unlocking is known, but he sounded an optimistic note.

The scientist, from Imperial College London, and a member of the Scientific Advisory Group for Emergencies (Sage), told BBC Radio Four’s Today programme: “We need to remain cautious, especially with the potential increase in contact rates again as the weather becomes less fine and schools return.

“We’re not completely out of the woods, but the equation has fundamentally changed.

“The effect of vaccines is hugely reducing the risk of hospitalisations and death.

“And I’m positive that by late September or October time we will be looking back at most of the pandemic.

“We will have Covid with us, we will still have people dying from Covid, but we’ll have put the bulk of the pandemic behind us.”

Daily reported cases fell for the seventh day in a row to 23,511, the latest Government figures on Tuesday showed.

Their official statistics also showed a further 131 people had died within 28 days of testing positive for Covid-19, the highest day-on-day rise since March 17, although figures early in the week are usually higher due to a lag in reporting at weekends.

It brings the UK deaths total to 129,303, although separate figures published by the Office for National Statistics show the total number of deaths with Covid in the UK has now reached 154,661.

Responding to the Government figures, Dr Yvonne Doyle, medical director at Public Health England, said: “Rates are still high and the pandemic is not over yet, today we have recorded the highest number of deaths since March.

“This is in part due to the high number of cases recorded in recent weeks.

“We know deaths follow when there are a high number of cases and data today highlights we are still in the third wave.”

A number of factors are thought to be behind the recent fall in cases, including increased vaccination, people socialising outdoors and a stop to secondary school testing, which was picking up symptomatic and asymptomatic cases.

Due to the time lag between reported cases and people being admitted to hospital, admissions for treatment are still rising, but the figure is still well below levels seen in the second wave of the pandemic.

Meanwhile, the continuation of US restrictions on international travel has dashed British holidaymakers’ hopes of travelling across the Atlantic this summer.

Policing minister Kit Malthouse said the decision by the US government not to loosen its rules was “disappointing”, but not surprising.

He told Sky News: “Obviously that is for them to assess and we are assessing the likelihood of variants coming in from other countries as well.

“So, it doesn’t surprise me that they are doing similar.

“It is obviously disappointing.”