The vaccination programme has been hailed as “an incredible achievement” by Health Secretary Matt Hancock.
It comes as the latest weekly surveillance report from Public Health England (PHE) shows that Covid-19 case rates in all regions of England are continuing to increase.
PHE said case rates in England among all age groups are continuing to rise and the highest rate is among 20 to 29-year-olds, with 195.9 cases per 100,000 people in the seven days to June 13, up week-on-week from 123.6.
The second highest rate is among 10 to 19-year-olds, up from 100.3 to 143.3, while for people aged 60 and over the rate is 14.3, up slightly from 10.6.
‘An incredible achievement‘
Matt Hancock said: “As of this afternoon we have given a first dose of vaccine to four out of every five adults in the United Kingdom.
“And the speed of deployment means that tomorrow we can open vaccination to everyone over the age of 18.
“I think it’s an incredible achievement on the vaccination side.”
How to book your vaccine
To book your vaccination appointment, go to the NHS website here.
The news that all adults in England can now book their Covid-19 jabs comes after the final step to lockdown lifting in the country was pushed back by four weeks.
The Prime Minister confirmed earlier this week that lockdown measures would remain in place until 19 July - pushed back from 21 June - due to the rapid spread of the Delta variant.
The four-week delay intends to allow more people to get vaccinated.
The Department of Health and Social Care said 42,216,654 people across the UK have now been vaccinated with a first dose (80%), while 30,675,207 people have had both doses (58%).
What’s happening in Scotland, Wales and Northern Ireland
In Northern Ireland and Wales, the Covid-19 vaccination programme is already open to those aged 18 and over.
In Scotland, all 18 to 39-year-olds are being invited, with older age groups first, in the specific areas of Glasgow affected by the current outbreak.