Delays at Heathrow airport have been described as “unacceptable” by the Home Office, af reports of passengers fainting in queues of up to three hours.

Border staff were left dealing with a huge backlog of travellers, with witnesses saying they had seen people – including a pregnant woman – passing out while queueing.

The Home Office criticised UK Border Force, its own immigration agency, and said the long waiting times for passengers were “unacceptable”. It added that Border Force was reviewing its rosters and “flexibility” to help deal with the issue and improve queueing times.

A spokesperson said: “Throughout the pandemic we have been clear that queue times may be longer as we ensure all passengers are compliant with the health measures put in place to keep the UK public safe. However, the very long wait times we saw at Heathrow last night are unacceptable.

“This is the busiest weekend of the year for returning passengers, with particularly high numbers of families with children under the age of 12, who cannot use e-gates. Border Force is rapidly reviewing its rosters and capacity and flexibly deploying our staff across the airport to improve waiting times.

“We are working very closely with Heathrow Airport and its airlines and we are all committed to making sure all passengers can have a safe and hassle-free journey.”

One holidaymaker, Sonny Singh, told Sky News that he saw a pregnant woman faint while queueing in the airport on Friday night. He said: “There were thousands of families queueing and just two people in booths up front checking documents.

“Children were screaming and crying. The queue moved about five feet in the space of about 45 minutes. Then, when the pregnant woman fainted, it finally got through to someone somewhere – the kids were then put on the side to sit while the adults waited in the queue and it began moving faster.”

Singh said his family left Heathrow shortly after midnight after a three-hour wait, by which time the trains had stopped running.

Another passenger caught up in the chaos said he and his pregnant wife had to wait for two hours after returning from their holiday in Malta. Jason Reed told Sky News: “Honestly, it was absolute carnage. My wife is pregnant and has a bad back so was really uncomfortable and tired.”

A Heathrow spokesperson said: “We are very sorry that passengers faced unacceptable queueing times in immigration due to too few Border Force officers on duty.

“Border Force were aware of the extra demand from families and we are very disappointed that they did not provide sufficient resource.

“We have additional Heathrow colleagues to support in managing queues and to hand out passenger welfare including water but we need every immigration desk to be staffed at peak times.

“We have escalated this with Border Force and expect them to provide a better service over the remainder of the weekend.”