The landmark was announced by Health Secretary Matt Hancock and Prime Minister Boris Johnson on Monday as the country looks forward to the next phase in the easing of restrictions to curb the spread of the disease on May 17.
Posting on Twitter on Monday afternoon, Mr Hancock hailed what he described as a “massive achievement”.
“We’ve just delivered the 50 millionth jab across the UK!” he wrote.
“Massive achievement from the team. These jabs are saving lives and helping us get back to normal. Thank you to everyone who has played their part in our national effort. When you get the call, get the jab.”
Speaking during a campaign visit to Hartlepool around lunchtime, Mr Johnson told reporters: "As things stand, and the way things are going, with the vaccine rollout going the way that it is - we have done 50 million jabs as I speak to you today, quarter of the adult population, one in four have had two jabs.
"You are seeing the results of that really starting to show up in the epidemiology.”
Mr Johnson also gave a clear signal that international travel will begin on May 17 and backed the scrapping of social distancing rules in late-June.
"I think that we will be able to go ahead, feels like May 17 is going to be good.
"But it also looks to me as though June 21 we'll be able to say social distancing as we currently have to do it, the one-metre plus, I think we have got a good chance of being able to dispense with the one-metre plus from June 21.
"That is still dependent on the data, we can't say it categorically yet, we have got to look at the epidemiology as we progress, we have got to look at where we get to with the disease. But that's what it feels like to me right now."
On Sunday, Foreign Secretary Dominic Raab said "some safeguards" may stay in place when legal restrictions end, such as continued use of masks and physical distancing.
Last month, Government scientific advisers said the public should be able to remove face masks over the summer as vaccines do the heavy lifting in controlling Covid-19 - but they cautioned that masks and possibly other measures may be needed next autumn and winter if cases surge.
London passed the 5million mark for Covid-19 vaccines last week. NHS England data released on Monday afternoon showed a total of 5,163,040 jabs were given to people in the capital up until Sunday, including 3,622,076 first doses and 1,540,964 second doses.