Health Secretary Matt Hancock made the announcement in a video on Twitter, saying: “I’m absolutely delighted that over 20 million people have now been vaccinated.”
In mid-February, the UK met a government target of 15 million of the most vulnerable people receiving first doses.
The government says it plans to offer a first jab to the whole adult population by the end of July
Only Israel and the United Arab Emirates have vaccinated more people per head of population.
Smiling, Hancock said “I want to thank every single person who has come forward to get the jab,” calling this “the route out of this for all of us.”
“There’s a long way to go but we’re making big strides,” he said.
The UK’s vaccination programme has rolled out fast since its start in early December, when it became the first country in the world to begin mass inoculation with a fully trialled vaccine.
Earlier failures in contact tracing and controlling the spread of infection saw cases soar in the UK and the country’s death toll of 122,705 is the highest in Europe.
The country is still under national lockdown but daily cases, hospitalisations and deaths have all fallen dramatically since late January, despite the emergence of a more infectious variant.
On Thursday, Britain lowered the country’s virus alert level down one notch from the highest possible, saying the fall in cases had reduced the threat to the state-run National Health Service.