Others claimed staff failed to go to work yesterday because of the Euro final the night before as hundreds of people crammed in front of the departure gates at Terminal 5.

       One person tweeted: "Total chaos at Heathrow Airport security this morning - [British Airways] staff telling passengers it's due to many security staff failing to show."

       Another said: "Chaos at Terminal 5 this morning, 90 minutes to go through security.

       "British Airways staff nowhere to be seen, just like social distancing. Hundreds must have missed flights."

       Pictures showed crowds unable to social distance but most wore masks while trying to get through security.

       A Heathrow spokeswoman said: "We had some passenger congestion in Terminal 5 departures due to colleagues being instructed to self-isolate by NHS Test and Trace.

       "We have activated additional team members to assist passengers with their journeys and the operation has now returned to normal.

       "We apologise for any inconvenience caused."

       The NHS COVID-19 app has come under fire with thousands of people deleting it because of its "sensitivity".

       Businesses have been crippled by employees notified to self-isolate.

       And the Government has considered making doctors and nurses exempt from the app's alerts.