Gov.uk recommends consumers register with the app “before booking international travel” and said it was working with devolved administrations “to ensure this facility is available to everyone across the UK”.

A paper version will also be available by dialling 119, the Covid testing helpline. “This must be at least five days after you’ve completed your course of the vaccine. We expect the letter to take up to five days to reach you,” it said. It added GPs were unable to issue these letters.

The NHS app is separate from the NHS Covid-19 app, which is used for contact tracing. 

The government recommends travellers register with the app at least two weeks before travelling. Those aged 13-15 will need to contact GP surgeries to request access to GP online services.

However, the website points out “not many countries” currently accept vaccination proof such as the app, adding: “For the time being most people will still need to follow other rules when travelling abroad. You may still be required to show other proof such as a negative PCR test and you may still have to isolate on arrival.”