Passengers were delayed for several hours at airports across the UK as self-service passport gates stopped working.
Heathrow, Manchester, Stansted and Edinburgh airports all reported problems with e-gates due to a technical issue.
The gates – managed by UK Border Force – allow travellers with biometric passports to pass through border control without a manual inspection.
The problem appears to have started at around noon on Friday.
The Home Office said at 2.30pm the issue had been resolved.
A Heathrow spokesman said: “Earlier today, a systems failure impacted the e-gates, which are staffed and operated by Border Force.
“This issue, which impacted a number of ports of entry, has since been resolved and the e-gates at Heathrow are back up and running again.
“Our teams remain on hand and are working with Border Force to monitor the situation, and to get passengers on their way as quickly as possible.”
Edinburgh Airport said earlier the problem was “nationwide”.
Documentary maker Louis Theroux was among passengers forced to wait in a long queue.
He wrote on Twitter: “Human logjam at Heathrow – apparently all the e gates at all the airports are down? That’s what the man just said.”
Other arriving passengers said they were being held on board aircraft due to the problem.
One traveller described Heathrow as a “joke” and predicted it would take him “four hours to get out”.
The Home Office said: “This afternoon a technical issue affected e-gates 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.”