On Tuesday, Lucy Moreton of the Immigration Services Union (ISU), which represents border immigration and customs staff in the UK, told MPs of the practical challenges in implementing the government’s strategy for preventing people with Covid-19 from entering the country.

Moreton said that vaccine certificates were proving “very easy” to forge and that, in many cases, officers simply had no way of checking whether the documents were indeed real. Asked how agents verified the documents, she said “it’s predominantly taken on trust,” adding: “We do get 100 or more a day of fake Covid certificates – that we catch.”

Moreton said that of the 20,000 people entering the UK every day, most of them were hauliers.

She added that the queues at airports may well be a “breeding ground” for the virus and that there was “little to no” evidence as to whether people were adhering to quarantine rules.

While foreign travel for holidays is banned across the UK, people can still leave and enter the country for business purposes. On Monday, England added India to its extensive “red list”, meaning people trying to enter the country from there will either be turned away or made to quarantine in a government-approved hotel for 10 days, due to concern about a new Covid variant first detected in India.

Scientists have expressed concern that variants, like those from South Africa and Brazil, could minimise the impact of the UK’s vaccination programme by being more resistant to antibodies. More than 500 cases of the South African strain have been identified in the UK.