Vaccine details were loaded onto to the app in time for travel’s restart on 17 May. The app, which is different from the one used for contact tracing, now has more than 4.8 million users. 

It is one of the first internationally compliant systems in the world to demonstrate vaccine status and has been designed in line with World Health Organisation interim guidance.

Those in England who have had two doses of any approved vaccine and who cannot use the app or are unable to access digital services, can call 119 and request a letter of proof. The first 20,000 letters were delivered in England on Saturday.

Health secretary Matt Hancock said: “The pace [at which] we’ve brought this to fruition is unparalleled and it is bringing immediate benefits to our wider health service. I encourage everyone to download the NHS app, it will help you access a host of services.”

The app also saw more than 11,000 register for organ donation in four days, 10 times the usual average.

Matthew Gould, NHSX chief executive, said: “This has been stood up in a matter of weeks, by a team working every hour to ensure we delivered a user-friendly service on time.

“We are really pleased with how it’s been received, and even more pleased to see it get so many people using the online services of the NHS.”