Heathrow descended into chaos as passport e-gates failed for the third time in three months on Wednesday morning.
Photographs on social media showed large crowds of travellers amassing outside the UK border as people took to Twitter to complain about the lengthy queues.
Passengers arriving into the airport were caught in queues which stretched for as long as two hours after a software failure caused the automated gates to break down.
“We are working to resolve the issue as soon as possible and apologise to all passengers for the inconvenience caused,” they added.
Among the sea of comments on social media, one wrote: "Bloody massive queue, and no real additional staff to be seen.”
— Lee Woodcock (@ltwoodcock) November 10, 2021
Bloomberg reporter Sid Philip wrote on Twitter: “Another day, another outage at Heathrow. 2 hours from plane to outside the terminal and I was lucky!
“The bizarre bit was for about ten minutes none of the counters were manned as the agents laughed, stood up and left!”
One Border Force officer at the airport, who asked to remain anonymous, told The Times the frequent failures were a source of growing frustration among staff.
They said: "It’s happened a few times this year. It’s very irritating as the hall would be half empty if they were working. It’s the joys of technology.”
Good(?) Morning... Here's a picture from T5 at 0730... No E-gates working. Lovely end to our first family holiday... 😩 pic.twitter.com/ZImb8LOQG3
— Jonathan Rudling (@JonRudling) November 10, 2021
There are more than 270 e-gates across 15 air and rail ports in Britain.
They have been available for use by UK citizens and EU nationals since 2008.
In May 2019, the system was expanded for use by nationals from Australia, New Zealand, Japan, Canada and the US.
When e-gates fail, passengers must be processed manually by Border Force officers but a shortage of staff has led to delays in recent months.
It marks the third software outage at the airport in as many months, with previous failures reported in September and October.
The delays threatened to disrupt the long-awaited lifting of travel restrictions to the US which reopened to British nationals on Monday.
Airlines have reported a surge in bookings since Joe Biden gave the green light for double-vaccinated travellers last month.
A total of 3,688 flights are scheduled to operate between the countries this month, according to travel data firm Cirium.
That is up 21 per cent compared with October but remains 49 per cent down on the pre-pandemic levels of November 2019.
Heathrow Airport has been approached for comment.