Britain’s electronic passport gates failed on Friday morning, causing chaos at airports across the country as incoming passengers were forced to queue for several hours.
Heathrow, Gatwick, Stansted and Manchester were among 15 airports hit by the "technical" failure in the e-gates which are used to read passengers’ passports on arrival.
The gates allow travellers with biometric passports to pass through border control without a manual inspection.
It meant Border Force officers had to revert to checking passengers travel documents manually, causing queues of up to four hours.
Heathrow tweeted: "Queue times are at unacceptable levels. Border Force are working to process passengers and we have called on the UK Government to address the problem as a matter of urgency, we do appreciate your patience."
The e-gates were shut down during lockdown and were closed when foreign travel resumed on May 17 so that they could be updated to be able to read the new passenger locator forms.
They were brought on line during the summer to replace manual checks but passengers returning to the UK still faced queues of up to six hours. It is understood more than 200 of the 270 have been upgraded but all 270 are thought to have been affected by the IT failure.
The Home Office said: “This afternoon a technical issue affected eGates at a number of ports. The issue was quickly identified and has now been resolved.
"We have been working hard to minimise disruption, and apologise to all passengers for the inconvenience caused.”
A spokesman added: "We are aware of a systems failure impacting the e-gates, which are staffed and operated by Border Force.This issue is impacting a number of ports of entry and is not an isolated issue at Heathrow.
"Our teams are working closely with Border Force to find a solution as quickly as possible."
There are 270 e-gates across the country at 15 air and rail ports, according to the government. It is understood all of them were hit by the failure.
A Stansted spokesman said: "Unfortunately, we are currently impacted by the national outage of UK Border Force e-gates. We are working hard alongside UKBF to process passengers as efficiently as possible."
Edinburgh Airport said: "The UK Border Force IT issue is nationwide and UKBF teams are working to resolve this.
"All available UKBF staff are in the arrivals hall to carry out necessary checks and allow passengers to pass through the border as quickly as possible. Thank you for your patience."
'Human logjam at Heathrow'
Documentary maker Louis Theroux was one of those at Heathrow waiting with his face mask on amid the queues. He tweeted: "Human logjam at Heathrow - apparently all the e gates at all the airports are down? That’s what the man just said."