The milestone has not yet been reached in Scotland but is fast approaching, with more than 48 per cent of adults given two doses.
Across the UK as a whole, latest figures show 50.2 per cent of over 18s have been fully vaccinated.
Data broken down by nation is slightly less up to date, but shows that as of June 1, 47.5 per cent of adults in Scotland had been given two doses. That figure was 50 per cent in England, 46.5 per cent in Northern Ireland and 45.1 per cent in Wales.
In Scotland, 2,137,618 people have had both doses, while 3,305,812 have had a first dose – just under three quarters of the adult population.
The programme in Wales has recently sped up significantly, with 85.3 per cent of adults given a first dose, compared to 74.7 per cent in England, 74.1 per cent in Scotland and 73.1 per cent in Northern Ireland.
UK health secretary Matt Hancock said he was “thrilled” at the UK-wide result.
“Shortly after vaccinating three quarters of adults with a first dose, I'm thrilled that we have now vaccinated over half of adults with the life-saving second dose,” he said.
“We know how important the second dose is to give protection, particularly against the Delta variant. That's why we’ve brought forward appointments from 12 to eight weeks for the most vulnerable people.
“I encourage everyone who is eligible to join the millions who have the fullest possible protection from this virus. Let's roll up our sleeves and put this pandemic behind us, once and for all.”
Minister for Scotland Iain Stewart said: “This milestone highlights the amazing progress we are making right across the country in our fight against Covid-19.
“Our fantastic NHS is working tirelessly to administer first and second doses and to hear that half of all adults in the UK are now fully vaccinated is such good news.
“The UK Government is supplying vaccines for people in all parts of the United Kingdom – I’d encourage everyone to please take up the invitation to get the jab when it comes to help us all through this pandemic.”