An IT glitch at border controls caused four-hour queues and major disruption at UK airports yesterday.
There were reports of scuffles breaking out at London Gatwick and London Luton and angry passengers complained on Twitter about queues stretching "for miles".
Heathrow and other airports had to draft in extra staff to cope with the situation, which mainly affected non-EU passengers.
The fault on UK Border Force computers meant staff had to input passport details manually rather than simply scanning documents.
At Luton police were called to deal with ‘scuffles’ in the immigration hall but no arrests were made.
Dover, Southampton and other seaports were also affected.
The Home Office apologised for the problems and said engineers had been working through the night to resolve the issue.
This morning (Thursday) Immigration Minister James Brokenshire told the BBC the situation is "much improved" and said it was doing its best to keep waiting times to a mininum during the busy morning period.
Meanwhile, London City Airport was evacuated for almost an hour last night following a fire alarm from 7.10pm with planes grounded and arrivals diverted to Southend.
And in Los Angeles, flights were grounded for more than an hour yesterday due to a computer failure at an air traffic control centre.
British Airways said two of its three LA flights suffered minor delays but schedules are back to normal today.
