Thousands of airline passengers faced long delays and flight cancellations at the end of the busy summer bank holiday weekend after a lengthy failure in the UK’s air traffic control system on Monday grounded hundreds of aircraft. National Air Traffic Services (Nats) said it had identified and remedied a “technical issue” that hit its ability to automatically process flight plans, but the knock-on effects were set to cause continued disruption to services as airlines and airports scrambled to reorganise flights this week. The problem severely restricted the number of aircraft allowed to land and take-off across the country as Nats was forced to input flight plans manually during the outage. The chaos came on one of the busiest days of the year, with holidaymakers returning to the UK on the final day of the bank holiday weekend, days before the new school year begins. Thousands of passengers were faced with hours-long delays stuck in crowded departure halls, including families with children unable to return home, some having to rebook for another day. Others were trapped on planes on the tarmac awaiting further information about whether their flights would be able to take off.

The delays unleashed a torrent of frustrated posts on social media from stranded travellers. Chris McLaughlin, the former co-chair of the UK Spaceflight Safety and Regulatory Council, wrote: “Bank Holiday Monday and where better to be than the BA Lounge at Heathrow. Air Traffic Failure over UK and my flight pushed to late afternoon — maybe.” London Heathrow, the UK’s busiest airport, said the disruption had affected services across the country. It said schedules would “remain significantly disrupted for the rest of the day” even though the problem had been fixed, and passengers should check their flights were still operating before leaving for the airport. British Airways said its schedule had been “severely disrupted” and warned it would have to make “significant changes” to its timetable. It said passengers on short-haul services should check the status of their flights. John Strickland, an aviation analyst, said “hundreds of thousands” of passengers would be affected by the problem. He said the disruption would likely spill into the next few days as airlines rearranged their planes and flight crews

It’s an enormous problem given the complexity on what should be a gold-mine period for UK airlines,” he added, warning of the financial impact on airlines of having to rebook passengers and reorganise their schedules. Ryanair warned the problems were affecting “all airlines operating to and from the UK today” and said it would delay or cancel “a number of flights” as a result.