Tens of thousands of passengers will wake up on Saturday where they had no intention of being after a security scare forced the evacuation of a large part of London’s Gatwick Airport.

At 8:20 a.m. on Friday, staff at the South Terminal discovered a “suspected prohibited item” in a passenger’s cabin baggage. At 10.55 the police had ordered a security cordon and evacuation of the building and the adjacent railway station.

At the world’s busiest airport with one runway, the plans began to unravel immediately for many to take off.

Those who had already checked in and passed security could remain “airside”, and many flights departed with fewer passengers than planned.

But other passengers were ordered to leave the building. Some sought shelter from the bitterly cold weather in parking lots while others walked to the North Terminal – about 15 minutes away.

Check-in at the South Terminal was interrupted for more than four hours.

North Terminal – the main base for easyJetEmirates and Tui – continued to operate but many passengers had severe problems reaching the airport. Gatwick has the UK’s busiest airport rail station, with more than 50,000 passengers using it on an average day; while trains continued to run through it, they were unable to stop during the security alert.

Thameslink trains added an extra stop at Horley, a small commuter station in Surrey, from which passengers could walk to the North Terminal in 30 minutes – or pay a reported £30 for a two-mile journey.

Eve and Alessandro, a couple from south London, were booked on Ryanair’s lunchtime flight to Alicante. They arrived at another nearby station, Three Bridges, and took a taxi to the only part of the airport they could access, the North Terminal.

“We’ve been waiting here for hours and our flight just keeps getting pushed back,” Eve told me The Independent.

Their flight eventually left three hours behind schedule.

Meanwhile, thousands of confused passengers arrived by air at the North Terminal. Arriving planes could park at the south terminal’s gates, but from there passengers needed to be bussed to the north terminal for treatment. Once through and into international arrivals, they discovered that there were very few options for onward travel.

Bomb disposal officers “made the package safe” and “two people who were arrested … have since been allowed to continue their journeys”, Sussex Police said.

Finally, at 2:45 p.m., the South Terminal was cleared to reopen. But before departing passengers could be re-entered, security staff and UK Border Force had to return to their positions.

The traveling public was allowed back in just after 3pm, as long queues formed at check-in and service desks, with a large number of distraught travelers told theirs was among the more than 80 flights that had been canceled – many on British Airwaysbut with Vueling, Wizz Air and Ryanair also founds aircraft.

Nadira, a British Airways passenger to Malta, was told at 3pm that her flight had been canceled and that she would be traveling on Saturday instead.

“Everything has been handled poorly, with no idea what’s going on,” she said. “Terrible communication.”

Once again, the lack of slack in the UK’s aviation infrastructure system has been exposed – as airlines face a multi-million pound bill in passenger care costs and lost revenue.