A group of charities is urging Boris Johnson to “swiftly clarify” how many Covid vaccine doses the UK is prepared to donate to poorer countries.
Save the Children and the Wellcome Trust are among those calling on the PM to start donating jabs through Covax.
This scheme aims to provide jabs for low and middle-income countries.
Culture Secretary Oliver Dowden said the UK does not currently have a surplus of vaccines, but when it does that surplus will be shared.
The UK, which has ordered 400 million vaccine doses and will have many left over, has said it will donate most of its surplus vaccine supply to poorer countries.
The lower income countries most likely to receive the first vaccines through Covax include Afghanistan, Haiti, DR Congo, Ethiopia and Somalia.
So far, more than 29 million UK adults have received a first dose of a Covid vaccine.
In a letter, the charities say the UK is “one of the world’s highest per-capita buyers” of vaccines and is on track to have more than 100 million surplus doses.
“There is therefore the high risk that the UK will be hoarding limited supply whilst health workers and the most vulnerable in low and middle-income countries do not have access,” the letter says.
“The UK will be sitting on enough surplus vaccine doses to vaccinate the world’s frontline health workers twice over.”
The group urges the UK to immediately begin donating doses through the Covax initiative.