Travellers have suffered long delays at airports such as Heathrow, Gatwick, Stansted and Birmingham due to a fault with UK Border Force computers.
The problem began yesterday with ports such as Dover and Southampton also affected.
The Home Office said security remained a "priority", and that it was still trying to fix the problem.
A spokesman for Gatwick told BBC News that queues had reduced overnight and it was "business as usual" for passengers.
“Yesterday’s difficulties with Home Office IT systems have now been resolved,” Gatwick tweeted this morning.
The glitch meant that UK Border Force staff were forced to input passport details manually rather than simply scanning documents.
The delays had a particular impact on non-EU passengers, and extra staff were called in to try to reduce the queuing time.
Queues of almost two hours were reported by an arriving passenger at Luton airport last night.
A Border Force spokesperson said: "We are currently experiencing temporary IT problems which may add to the time taken to conduct passport checks.
"We are working to rectify this issue and are providing extra staff to get passengers through the controls as quickly as possible. Our priority remains security of the border."
A Heathrow spokesman said: "There are some longer queues than normal in the terminals, but we have spoken to border force and they are putting on extra staff.
"Obviously we want to sort the issue out but not risk the integrity of the border controls."
Manchester airport said queues had gone down after some passengers experienced a small delay.
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