Based on the prevalence of Covid-19 in the UK and overseas, and accounting for quarantine compliance, Oxera and Edge Health say their findings suggest a single test would be appropriate for arrivals from countries categorised medium-risk as a consequence of either their Covid caseload or vaccination rate.

These countries, Oxera and Edge believe, could be designated "amber" if the UK government was to press ahead with a traffic light system to categorise risk when international travel resumes.

The research partners say many of the quick and inexpensive antigen tests on the market, were they to be deployed at the border, offer more effective screening than mandatory quarantine when taking compliance into consideration.

Oxera and Edge were commissioned last year by British Airways owner IAG, Virgin Atlantic, Heathrow airport, Manchester Airports Group and Iata to investigate whether the government’s own evidence base had underestimated the effectiveness of a single antigen test on arrival.

According to the government’s Scientific Advisory Group for Emergencies (Sage), rapid testing on arrival would only screen 11% of infectious travellers.

Oxera and Edge’s latest findings have been submitted to the government’s Global Travel Taskforce ahead of its 12 April report on how international travel can be reinstated safely and robustly.

Additionally, the study suggests a two-test strategy could be used to restart travel to and from higher-risk, or "red", countries; this would involve an antigen test taken up to 72 hours prior to departure, and three days’ quarantine upon arrival with a PCR test requirement.

This, Oxera and Edge assert, would be equally as effective as a double PCR test requirement, and would also ensure the government is able to track and sequence each strain of Covid-19 entering the UK.

Antigen testing for Covid is considerably quicker and cheaper than PCR testing, which requires laboratory analysis, and airports and airlines believe antigen testing could be more easily integrated into the passenger journey. However, there remains some debate as to which form of testing offers greater accuracy, or an acceptable trade off between accuracy and speed.

"The ultimate goal for governments must be to return to frictionless travel between countries that are considered lower-risk," said Michele Granatstein, Oxera partner and head of its aviation division.

"The vaccine roll-out, combined with internationally agreed standards on digital solutions to evidence Covid-status certification, will be intrinsic to that, but people should be able to travel safely, with or without a vaccine.

"Our analysis of the effectiveness of different quarantine and testing strategies shows the UK government can safely restart international travel at scale while tailoring test requirements and restrictions on a country-by-country basis."

George Batchelor, co-founder and director of Edge Health, added: "When the skies reopen, it’s clear a proportionate Covid-19 testing regime will remain an effective line of defence to support international travel to and from the UK.

"Given the success of the UK vaccination programme, and in line with the UK government’s risk-based approach to the wider economy, any restrictions should be targeted at reducing the potential import of variants of concern.

"Our modelling demonstrates that a single antigen test for medium-risk countries and dual-test approach for higher-risk countries, combined with three-day quarantine, could be an effective strategy to protect public health, while removing the burden of a 10-day quarantine."

Virgin Atlantic chief executive Shai Weiss said: “We believe international travel can safely restart at scale using a risk-based, phased easing of testing requirements and border restrictions that follows scientific evidence.

"In parallel to the world-leading UK vaccination programme, seamless travel between the UK and lower-risk destinations – such as the US, Caribbean and Israel – must remain the objective, enabling the free movement of people and goods vital to the UK’s economic recovery.

"When applied to the government’s proposed traffic-light framework, this new modelling demonstrates how robust and proportionate testing strategies can be applied to amber and red countries."