A senior director at Public Health England (PHE) has said she hopes the delay to the end of lockdown will allow time for everyone over the age of 40 to get double vaccinated.

Dr Susan Hopkins, strategic director for Covid-19 at PHE, said getting as many people as possible jabbed by July 19 should mean the latest wave in Covid-19 cases caused by the Delta variant will not be as deadly as previous waves.

Last week, the Government was forced to delay so-called Freedom Day, when all restrictions will be lifted, by four weeks due to a worrying rise in positive tests.

Read more: As third Covid wave 'definitely' hits, here's the case rate for every English town and city

Speaking to the BBC's The Andrew Marr Show, Dr Hopkins said: "The extra time to vaccinate more people, get two doses of vaccination in as many people as possible, will hopefully mean that what we're seeing with this wave won't look the same as the previous waves that we've seen in this country."

She continued: "What I would like to see is that everyone over the age of 40 has had the opportunity to get double vaccinated.

"And as many people over the age of 30 have the opportunity to get two doses of vaccination as well.

"We know that two doses of vaccination really protects against hospital admission, about 94% overall and 92% for AstraZeneca and 96% for Pfizer.

"Overall, as many people getting two doses of vaccination would be really good."

She added: "We should be able to hit the 70% figure having two doses before July 19."

Dr Hopkins also said that in some areas where the Delta variant had been most prevalent there were signs the virus was being brought under control by the vaccination programme.

But this has been offset by rises elsewhere.

According to PHE data there has been a 79% rise in one week in cases of the Delta variant, first identified in India, with the increase being driven by younger age groups.

Dr Hopkins also suggested holidaymakers returning from abroad who have been double vaccinated might be able to avoid isolation.

She said scientists would be looking at data from other countries, particularly Israel, where they are considering allowing those visiting the country who have had two jabs to skip quarantine.

"We will need to be alert and will need to consider how we can measure the response of these vaccines to new variants that come along," Dr Hopkins said.

"I think that in a time in the future, I'm not sure when, I can imagine a situation where we will have alternatives to isolation for people who have two doses of the vaccine."

Overnight it emerged that more than 700,000 Covid-19 jabs were booked in a single day when the NHS vaccination programme was opened up to those aged 18 to 20.

People in England made 721,469 appointments through the national booking service on Friday, more than 30,000 an hour or more than eight every second, PHE said.

It comes as PHE's regional director for London said that people living in the capital will need to build resilience ahead of July 19.

Professor Kevin Fenton said it was unlikely the capital would have all over-30s double vaccinated due to lower take-up in the age group.

He said: "Get the first dose in as soon as possible because even with the first source, there is some protection that you will receive.

"We're in the foothills of what could possibly be a third wave, we should be doing the hands, face, space, ventilate, prevention.

"And we (will) continue to practise those preventive measures - vaccinating now won't stop the rises we are seeing in the community this week, but they will begin to build the resilience for the city as we get to July 19."

Find out the covid rates where you live here:

Meanwhile, health experts are warning of a "pretty miserable winter" in the UK with further lockdowns not ruled out.

An emergence of new respiratory viruses as well as the ongoing battle with the coronavirus pandemic could see the UK placed into another lockdown, say Sage scientists.

Professor Calum Semple, member of the Scientific Advisory Group for Emergencies (Sage), which advises the Government, says children and elderly people will be particularly vulnerable to endemic viruses by the end of 2021

And other health expert and Government advisors warned we could be facing winter lockdowns if hospitals become "overwhelmed" at some point as they continue to care for other winter bugs.

Prof Semple we will see a rise in bronchiolitis and "community acquired pneumonia" in children and the elderly.

On Sunday morning, Professor Semple told Times Radio: “I suspect we’ll have a pretty miserable winter because the other respiratory viruses are going to come back and bite us quite hard. But after that, I think we’ll be seeing business as normal next year.

He said that we can expect a "rough" July, August and then winter period and that there was heightened risk of the young and elderly being exposed to other respiratory viruses we do not yet have vaccines for.

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He said: “There’s a sting in the tail after every pandemic, because social distancing will have reduced exposure, particularly of pregnant women and their newborn babies, they will have not been exposed to the usual endemic respiratory viruses.

“The protection that a pregnant woman would give to their unborn child has not occurred.

“So we are going to see a rise in a disease called bronchiolitis, and a rise in community acquired pneumonia in children and in the frail elderly, to the other respiratory viruses for which we don’t have vaccines.

“So that’s why we’re predicting a rough July, August and then a rough winter period.”

Professor Semple called it the “fourth wave winter” but added it would be much milder than the previous ones.