British Prime Minister Boris Johnson (L) thumbs up after receiving the Oxford-AstraZeneca COVID-19 vaccine at St Thomas' Hospital in London, Britain, March 19, 2021. (Andrew Parsons/No 10 Downing Street/Handout via Xinhua)

There is "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," said a letter to the prime minister by those including British government science advisor Jeremy Farrar.

"The UK will be sitting on enough surplus vaccine doses to vaccinate the world's frontline health workers twice over," it said.

LONDON, March 28  -- British Prime Minister Boris Johnson is facing calls on Sunday to immediately begin donating vaccines to poorer nations or risk hoarding supplies while frontline workers are exposed to coronavirus, the Evening Standard newspaper reported.

British health and development charities urged the prime minister to take "accelerated action" and "swiftly clarify" how doses will be shared, according to the newspaper.

The appeal was contained in a letter to the prime minister by those including British government science advisor Jeremy Farrar and Save the Children UK, among others.

With more than half of adults having received a jab, they said Britain is "one of the world's highest per-capita buyers" of vaccines and is on track to have more than 100 million surplus doses.