Air travellers were being plagued by bank holiday flight chaos after the Home Office confirmed all E-gates were failing at UK airports.
The British government has now resolved to fix a technical problem that caused electronic border gates at airports around the country to stop working late on Friday.
The problems have led to hourslong waits for travellers leaving and entering the UK at the start of a busy holiday weekend. In some instances, passengers fainted.
It comes as technical issues were also causing problems at the Port of Dover, meaning major tailbacks on roads into the Kent coastal town.
Travellers posted photos of long lines at airports around the country as all incoming passengers were forced to use manned passport desks, instead of the automatic gates equipped with electronic passport scanners.
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Marc Baret had been booked on a flight from Chicago to Manchester via Heathrow.
He told the BBC he was left waiting more than two hours at the airport.
He said: "It was absolute chaos at passport control. There were people getting really frustrated and a couple of individuals tried to jump queues, the police had to get engaged and one of the passengers fainted."
A Home Office spokeswoman said that the Border Force had put in place "robust plans" to deploy officers to minimise disruption and wait times.
The automated e-gate system is available for British citizens aged over 12 and those from the EU, as well as people from several other countries including Australia, Canada, the US, Japan and New Zealand.
The spokeswoman said on Saturday evening the problem had been resolved, adding: "Following a technical border system fault which affected e-gate arrivals into the UK, we can confirm all e-gates are now operating as normal.
"We thank those travellers who were impacted for their patience and staff for their work in resolving the issue."
One traveller arriving at Heathrow posted on Twitter: "Just landed to scenes of utter chaos. 2 hour queues just to get to the real queue. Gates broken."
Another at Gatwick said it was an "utter joke", while another at Heathrow spoke of the "mother of all queues".
Lucy Morton, from the Immigration Services Union, warned that queues would build "very, very quickly".
"You end up putting all the passengers through physically-manned officer desks," she told the BBC's Radio 4.
"Staff can't take the breaks that they should be taking ... the whole thing will snowball very quickly."
She said between 60-80% of travelling passengers will go through e-gates, depending on the airport.
"There's no impact on national security," she said, adding all arrivals will still be fully checked.
"But it will build queues and that in itself builds its own set of problems. People becomes frustrated, they take it out on the staff.
"All of this will cascade during the day."
Jim Wheaton, 66, and his daughter Annie were among those stuck at Terminal Two at Heathrow Airport.
Annie missed the rehearsal dinner for a friend's wedding in Boston, USA, due to their British Airways (BA) flight being cancelled.
The problems come after British Airways had to cancel 175 flights following an IT failure on Thursday and Friday.
Meanwhile, long queues have been experienced at Dover which has also experienced IT problems.
The Port of Dover posted on Twitter: "Thank you for your patience as we catch up from earlier IT issues at border control, which have been resolved. Traffic now processing well through border. Average waiting times for cars and coaches now 90 mins."
A Gatwick Airport spokesman said the problem started on Friday evening but queues had eased on Saturday morning.
He said: "Some passengers may experience delays at immigration due to a nationwide issue with UK Border Force e-gates.
"Our staff are working with UK Border Force - who operate passport control including the e-gates - to provide assistance to passengers where necessary."
Heathrow Airport posted on Twitter: "We are aware of a nationwide issue impacting the eGates, which are operated by Border Force.
"This issue is impacting a number of ports of entry and is not Heathrow specific.
"Our teams are working closely with Border Force to help resolve the problem as quickly as possible and we have additional colleagues on hand to manage queues and provide passenger welfare. We apologise for any impact this is having to passenger journeys."
It's the third day in a row of air travel disruption, with British Airways apologising after being forced to cancel dozens of flights due to IT problems since Thursday.
BA said yesterday that cancellations were still happening due to the "knock-on effect of a technical issue" resulting in staff being in the wrong location.
