Holidaymakers could face delays of up to 45 minutes each at airports if they haven’t filled in their forms properly.
Border officials are braced for big queues when international travel finally resumes on Monday - despite drafting in the highest number of officers to Heathrow since the 2012 London Olympics.
Brits returning from holidays abroad will have to provide proof they had a test before travelling home, as well as details of which countries they visited.
Anyone who has visited a country on the UK’s green list will not need to quarantine when they get back.
But people who have come from red or amber list countries will have to isolate for up to 10 days on their return, either in a Government-backed quarantine hotel or at home.
Passport checks traditionally take between 25 to 75 seconds each but tough Covid restrictions mean the process will take longer to complete.
If people have failed to comply with the restrictions, the process could take up to 45 minutes as staff may have to issue fines.
Insiders said some people had been trying to flout the rules by using different passports or fake Covid-19 tests.
People heading on holiday on Monday are advised to make sure they have all the right documents for the country they are visiting to speed up the process.
Holidaymakers returning from amber list countries can expect a knock at the door to check they are complying with quarantine rules.
Private security staff have been drafted in to make sure travellers are obeying the quarantine rules, with capacity to check up to 10,000 people a day.
The contractors can report people to the police if they are flouting the rules.
