Waits in border queues at Heathrow Airport stretch up to six hours, it was claimed, causing travel misery for 10,000 passengers a day.
Britain's busiest airport is struggling with increasing passenger numbers and a shortage of border staff, leading to what one expert said were "untenable delays".
A traveller told The National he was forced to queue for six hours with minimal social distancing after arriving at Heathrow this week.
Joao Rocha said passengers were put at risk of coronavirus infection because of long waiting times and lack of ventilation.
In hotel quarantine, Mr Rocha said the scenes at Heathrow on April 11 were shambolic and left him feeling angry and upset.
"Everybody, it doesn't matter where they were from, we were standing stand very close to each other," he said.
Mr Rocha, a British citizen who runs his florist business in central London, returned to the UK from Brazil where he looked after his father, who has dementia.
He says there were only three Border Force officers to process more than 200 arrivals, many of whom had come from red-list countries with an elevated infection risk.
Pictures posted to Twitter by Mr Rocha show long, zig-zagging lines with passengers separated by just a thin barrier.
Heathrow responded to the tweet by saying social distancing was not always possible at every point of the airport journey.
It also called on the government to address the "unacceptable delays" at border control.
On Wednesday, Heathrow's chief solutions officer Chris Garton demanded that the government introduce quicker checks to help deal with the delays.
“We need to see a dramatic improvement in border performance if we are to increase passenger numbers travelling through Heathrow,” he told a parliamentary transport committee.
"The situation is becoming untenable."
Mr Rocha said the atmosphere at border control was tense and some Border Force officers did not wear masks, contravening government guidelines.
Staff took about 10 to 15 minutes to process each passenger because they must check Covid test results and whether the travellers are required to stay in hotel quarantine.
At one stage, a member of staff reportedly began to shout at agitated passengers and had to be removed by police to calm the atmosphere.
Mr Rocha said the staff member said masks did not work when asked why she was not wearing one.
"At some point I thought there would be some sort of fight or an argument," he said.
"It was really really, busy. I understand that staff are frustrated. I truly believe most of the people who were travelling had a really good reason to do so."
Mr Rocha said he sympathised with the pressures on border employees, but was led to feel that staff "didn't care" about passengers.
"I'm just really angry and frustrated, and actually the word is probably embarrassed," he said. "It was a total shambles."
Holidays abroad are banned by the government until May 17 at the earliest.
But under its new traffic-light system, travel to low-risk green countries could become quarantine-free after that date.
Some travel executives, however, voiced concerns over the requirement for passengers to red or amber countries to take two PCR tests – one before departure and another a day or two after their return to England.
The Association of British Travel Agents chief executive Mark Tanzer said the plan for reopening foreign travel was overcautious.
"Certainly for the green category, the PCR test is a sledgehammer to crack a nut," Mr Tanzer told the House of Commons transport committee.
"We'd like to have no testing but in the short term a cheaper, faster test, and if that were positive then you can proceed to a PCR test if necessary.
"Otherwise you are going to hobble the industry and you are going to stop people from travelling, even though they've been vaccinated."