The expansion of the vaccine drive coincided with the UK Health Secretary Matt Hancock's statement to the House of Commons, where the minister revealed that vaccines have averted an estimated 39,000 hospitalisations and more than 13,000 deaths in the country.

He also said that of 12,386 cases of the Delta variant – or the B1.617.2 variant first detected in India – 126 people were admitted to hospital and of these, 83 were unvaccinated, 28 had one dose and three had two doses.

“Every day brings with it another exciting milestone in our vaccination programme – the largest and most successful in NHS history,” said Hancock.

“The vaccine is saving lives and preventing hospitalisations. Two weeks after we extended the invite to all over 30s, we are now extending the offer to everyone aged 25 and over,” he said.

The National Health Service (NHS) has dubbed the latest expansion of its vaccination programme as the “Home Straight” phase, as around 3 million people aged between 25 and 29 will begin being invited to book their first vaccine dose.

The move comes as NHS data shows that more than half of all adults in the country are now fully vaccinated against COVID-19.

“We have one of the highest uptake rates in the world with over half of the UK population having the fullest possible protection from two doses, and over three quarters receiving at least one dose. The vaccine is our way out of this pandemic so when you get the call, get the jab,” said Hancock.

According to previously released expert advice, both doses of the COVID-19 vaccines are needed for strong protection against the Delta variant – which is now feared to be the dominant variant of concern (VOC) behind infections in the UK.

"It is too early to make decisions on step four, the road map has always been guided by the data and as before, we need four weeks between steps to see the latest data and a further week to give notice of our decision. So we'll assess the data and announce the outcome a week today," Hancock told the Commons, in reference to the June 21 timeline for an end to all lockdown restrictions.

Hancock also informed Parliament that he has asked the Joint Committee on Vaccination and Immunisation (JCVI) to provide clinical advice on the vaccination of 12-17-year-olds after the Pfizer/BioNTech jabs received regulatory approval for children last week.

Meanwhile, NHS England chief executive, Sir Simon Stevens, hailed the “watershed moment” of a further extension of the vaccination programme six months since 90-year-old Maggie Keenan became the first person anywhere in the world to receive her first dose on December 8, 2020.

“The NHS vaccination programme is a real team effort and it is a testament to NHS teams across the country, that we are able to open up to people in their twenties just six months on from delivering that world first jab to Maggie Keenan,” said Stevens.

“Getting the lifesaving COVID-19 jab is the most important thing you can do, with NHS staff vaccinating at over 1,600 sites including vaccine buses, places of worship, sport stadiums and other convenient locations,” he added.

The latest COVID-19 statistics released on Monday recorded one more death from the deadly virus in the UK and 5,683 cases of coronavirus infections within the community.