The health secretary hails the milestone as 32 and 33-year-olds are offered the jab.
More than 50 million coronavirus vaccine doses have now been given in England.
Figures released by NHS England show 31,546,846 UK adults have had their first jab, and 18,699,556 have had two.
Health Secretary Matt Hancock said the milestone came after “one of the biggest and most important national efforts in our history”.
People aged 32 and 33 in England are being invited to book their first vaccination from this weekend.
NHS England’s lead for the Covid vaccination programme, Dr Emily Lawson, said the rollout was “continuing at pace”.
“This success is the result of the tireless efforts of NHS teams, alongside local partners and volunteers, who are determined to protect their patients, families and communities,” she said.
“Despite this we must take nothing for granted so when you are invited please book your appointment – and, along with millions of others, get vital protection against coronavirus.”
A total of 50,246,402 Covid-19 first or second doses of vaccinations took place in England between December 8 and May 21, the data shows.
Across the UK more than 620,000 people had a vaccine dose on Friday, the latest government data shows.
A further 2,694 new cases and six deaths, within 28 days of a positive test, were also announced on Saturday.
Mr Hancock has said the government is on track to offer a first vaccine dose to all adults in the UK by the end of July.
The NHS opened bookings to about one million more people in England on Saturday morning.
Text message invitations are being sent out to 33-year-olds on Saturday and to 32-year-olds on Monday.
They will appear as a message from “NHSvaccine”, and people who cannot go online can call 119 to book a jab.
The other UK nations are already offering jabs to younger age groups – people aged 30 and over are eligible in Scotland, as are over-18s in Wales and over-25s in Northern Ireland.
People in their 30s and pregnant women are being offered either the Pfizer-BioNTech or the Moderna vaccines if they are available, rather than the Oxford-AstraZeneca jab, because of concerns about a possible link between the Oxford jab and rare blood clots.
Over-50s, and those considered clinically vulnerable, will have their second doses brought forward to eight weeks after their first, rather than 12, following concerns about the spread of the variant first discovered in India.
The variant – also known as B.1.617.2 – is responsible for the majority of new cases in pockets of England.
Bolton continues to be the worst affected area with 385 cases per 100,000 people.
But North Tyneside and parts of west London are among the latest areas to start surge testing of residents amid concerns at its spread.
Andrea Fallon, Rochdale’s director of public health, told BBC Radio 4’s Today programme the council was still focusing on priority groups as well as opening five drop-in centres as part of a “new programme”.
She said: “Once the virus gets into our communities it will take hold very quickly…. myself and our senior team have been working really closely with regional colleagues to put in place this surge vaccination programme this weekend.”
It comes as Germany announced that anyone arriving from the UK will have to quarantine for two weeks. German officials said the decision was related to the spread of the Indian Covid variant.