Prime Minister Boris Johnson is to urge leaders of other wealthy countries to commit to vaccinating the world against Covid-19 by the end of next year.
He will lay out a global target at a summit of the G7 group of advanced economies on Friday.
The US, France, Germany, Italy and Japan have all said how many doses they will donate to the global vaccine-sharing programme, Covax.
But the UK and Canada are yet to put figures on their planned contributions.
Meanwhile, former Prime Minister Tony Blair has called for people who have had both Covid jabs to get extra freedoms, including the right to travel abroad more easily.
This would encourage more vaccinations, he told BBC One's Andrew Marr Show.
Ahead of the G7 summit, which will take place in Carbis Bay, Cornwall, from 11 to 13 June, Boris said he would ask his counterparts to "rise to the greatest challenge of the post-war era" by "vaccinating the world by the end of next year".
"I'm calling on my fellow G7 leaders to join us to end this terrible pandemic and pledge will we never allow the devastation wreaked by coronavirus to happen again," he said.
Such an achievement would be the "single greatest feat in medical history", he added.
The summit will be the G7 leaders' first face-to-face meeting since the start of the pandemic, and US President Joe Biden's first visit to the UK since taking office.
The US has pledged to donate 80 million vaccine doses to poorer countries, while other G7 countries have offered much smaller numbers.
There has been frustration from campaigners that the UK has not specified how many it will pledge, but the prime minister is expected to do so at the summit.
The UK will also encourage more discussion about how manufacturing can be stepped up.
More than 40 million people in the UK (76.2% of adults) have had their first dose, according to the government's coronavirus dashboard. Some 27 million people have had two doses (51.6% of adults) and are fully vaccinated.
In England, the gap between doses was reduced last month from 12 to eight weeks for people over 50 and those with severe underlying health conditions.
