Britain prepared to start its biggest ever immunisation campaign but health officials warned the drive to inoculate millions against Covid-19 would be a “marathon” stretching well into next year.

The world-first rollout of the Pfizer-BioNTech vaccine is due to begin on Tuesday — dubbed “V-Day” by Health Secretary Matt Hancock, who has volunteered to take it live on television to assuage any public doubts over the rapid approval.

Croydon University Hospital in south London is one of 50 clinical hubs that started receiving the country's initial consignment of 800,000 doses over the weekend, from a Pfizer plant in Belgium, AFP reported.

The vaccine rollout coincides with the end-game of Brexit talks on Britain's future trading relationship with the European Union. The government reportedly has military flights on standby to transport the jabs from Belgium, in case the negotiations collapse and new rules cause border chaos from January 1.