New research, carried out at the end of July, found that only 0.4% of fully vaccinated air travel passengers tested positive for Covid-19 after arriving in the UK from abroad.
Single vaccinated travellers were found twice as likely to test positive, while between one and 1.2% of those travelling unvaccinated received a positive result.
The figures are now being studied by UK health secretary Sajid Javid, who is expected to review the current traffic light system on Thursday 26 August.
While there have been talks of replacing PCR tests with lateral flow tests for amber and green countries, founder of Cignpost, Nick Markham told The Telegraph that the tests are not accurate enough to rely on, with 400 people infected with Covid-19 still arriving in the UK daily.
