Britain is close to agreeing a 500 million pound ($624 million) supply deal with Sanofi and GlaxoSmithKline for 60 million doses of their potential COVID-19 vaccine, the Sunday Times reported.
The newspaper said that Britain was considering taking an option to buy the vaccine should it work in human trials, which are due to begin in September.
Sanofi was not immediately available to comment on the report, while a spokesman for GSK declined to comment.
A spokeswoman for Britain's business ministry, which is handling Britain's supply of potential Covid-19 vaccines, said talks were ongoing with different parties about access but did not confirm if the Sanofi/GSK project was among them.
"The Government's Vaccines Task Force is actively engaging with a wide range of companies both in the UK and abroad to negotiate access to vaccines," she said.
"Appropriate announcements of these arrangements will be made as and when agreements with any of these companies are finalised and signed."
Sanofi is working on two possible Covid-19 vaccines, one of which uses an adjuvant made by GSK to potentially boost its efficacy.
Its timeline for clinical trials is behind the likes of Moderna Inc, the University of Oxford in collaboration with AstraZeneca Plc, and an alliance of BioNTech and Pfizer Inc, whose projects all grabbed headlines by moving to human trials as early as March.
Sanofi and GSK have both said they are prioritising quality over speed in developing a vaccine.