More than 47m doses of COVID-19 vaccine have now been administered in total UK-wide since the NHS delivered its first jab on 8 December.
A total of 33,843,580 million people had received a first dose by the end of 26 April - 13,201,811 of whom had also received a second dose.
This takes the proportion of the UK adult population who have received a first dose to nearly two thirds - and the proportion who have received two doses to just over the 25% mark based on Office for National Statistics (ONS) population estimates.
Health and social care secretary Matt Hancock said the latest milestone was a 'terrific cause for celebration'. The announcement that one in four adults have received two doses of vaccine came as the NHS extended its offer of first doses to adults aged 42 and 43.
More than three quarters of vaccinations in England have been delivered by GP-led vaccination sites - a contribution that has ramped up pressure on the profession.
NHS England this week recognised the intense pressure on general practice as the profession manages the vast bulk of vaccinations on top of 'pent-up demand' unleashed as COVID-19 restrictions in the UK are eased.
However, GPs and practice teams have been warned to prepare for an 'uplift in bookings' for COVID-19 jabs as the vaccination campaign opens up to more patients aged under 50.
More than 10,000 lives were saved between December and March by the UK COVID-19 vaccination campaign, according to analysis from Public Health England (PHE) on the reduction in hospitalisations and deaths.
Figures published by the ONS and Oxford University shows that COVID-19 infections fell by 65% after the first dose of the Oxford/AstraZeneca or Pfizer/BioNTech vaccines, rising further after the second dose.
In people aged over 70, both vaccines reduce the risk of symptomatic disease by around 60% after a single dose according to PHE analysis - with the vast majority protected from hospitalisation or death.
Mr Hancock said: 'Over a quarter of all adults across the UK, including those most vulnerable to COVID-19, have now had two jabs, meaning they have received the strongest possible protection.
'Thank you to the brilliant NHS, volunteers, local authorities, armed forces and civil servants who continue to work tirelessly to vaccinate people as quickly as possible.
'There is undeniable evidence that vaccines are saving lives, significantly reducing hospitalisations and deaths. I urge all those who are offered an appointment to get their jab.'