A total of just 867,000 passengers passed through the airport last month, with 480,000 of these heading to Europe.
A spokesperson said: “The vast majority of Heathrow’s route network (60%) remains grounded, requiring a 14-day quarantine on arrival, preventing the UK from travelling to and trading with these countries.
“Airport testing could safely open up these routes and kick-start the UK’s economic recovery.”
The most badly affected areas last month were North America, with passenger numbers down 96% and Latin America and Asia Pacific, both down 94%. Aircraft movements as a whole were down nearly 72%.