More than 30 million Britons have had their second Covid-19 jab, health officials have said.

The Department of Health and Social Care said that 57.3% of UK adults (30,204,738 million people) had had their second dose while almost four in five (79.4%) had received one dose.

The vaccines offer the most protection after a person has received both doses.

The Prime Minister announced on Monday that so-called Freedom Day has been pushed back to allow for more people to get their second jab.

Boris Johnson also said that the vaccine timetable had been sped up so that all adults would be able to receive their first jab by July 19 and that over 40s would receive their second dose eight weeks after the first, instead of 12 weeks later.

Meanwhile, the vaccine booking system opened to 23 and 24-year-olds for the first time on Tuesday.

By the time all restrictions are due to be lifted on July 19, all over 50s and the clinically vulnerable should have had both vaccines, and overall two thirds of the adult population are expected to have received both jabs.

The head of the NHS in England said that the health service would “finish the job” of the Covid-19 vaccination programme to the “greatest extent possible” over the next four weeks during the extension of lockdown.

Sir Simon Stevens also told the NHS Confederation conference that he expected that over 18s would be able to book their first Covid-19 jab by the end of the week.

Health Secretary Matt Hancock said: “Second doses are increasingly vital, so this is an incredibly important milestone.

“Day after day, our vaccination programme reaches new heights. With over 30 million people across the UK now receiving a second dose, we are giving the fullest possible protection to our loved ones in the face of new variants.

“The strength of the union has never been clearer than in the UK vaccination effort. All four corners of this country have pulled together for one common purpose – to get the jab and fight this virus.

“I want to pay tribute to everyone right across the country who has answered our call to arms and rolled up their sleeves to get the jab. I encourage everyone over 23 to come forward and get the jab.”

Dr Emily Lawson, NHS England’s lead for the NHS vaccination programme, added: “It is fantastic that 30 million second doses of the Covid vaccine have now been administered, thanks to the non-stop efforts of NHS staff and volunteers in what has been the biggest vaccination programme in NHS history.

“It is absolutely crucial that people receive their second jab to ensure they have maximum protection against the virus, and I urge everyone to come forward and book theirs as soon as they are invited, or move their second dose appointment forward if contacted to do so.”

Mr Hancock said on Monday that 1.3 million people who are over 50 and 4.5 million over 40s have so far had a first jab but not yet a second.

A previous study by Public Health England (PHE) found that the Pfizer coronavirus vaccine is 88% effective against the Delta variant after two doses and the Oxford/AstraZeneca jab was 60%.

Both vaccines were 33% effective against symptomatic disease from the Delta variant, which was first found in India, three weeks after the first dose.

A separate study found that Covid-19 vaccines are “highly effective” in preventing hospital admission with the Delta variant of coronavirus.

PHE’s study of hospital admissions found that the Pfizer/BioNTech vaccine is 94% effective against hospital admission after just one dose, rising to 96% after two doses.

And the Oxford/AstraZeneca vaccine is 71% effective against hospital admission after just one dose, rising to 92% after two doses.