Queues stretching twice the length of the terminal and delays of up to two hours were reported at Stansted Airport, after an exit door mistakenly left open triggered a security hazard at the weekend.

A group of passengers arriving on a Ryanair flight from Lisbon at 9.20am on Sunday morning went through “the wrong door” and ended up mixing with those departing for a flight, meaning all passengers in the departure lounge needed to re-screened.

Thousands then faced delays, with exasperated passengers taking to Twitter to express their frustrations.

Rob Treloar tweeted, along with a picture of the ensuing chaos: “Pandemonium at Stansted airport. Security queue stretches length of terminal twice!”

Duncan McKay wrote: “Ongoing security ’issue’ at Stansted airport. Massive queues as no one can get through security. Communication over PA has not been great.”

Tom Wallace added: “Yet again, Europe’s favourite ’airline’ delivers. Shambolic, I think would be the word of choice.”

A spokesman from Stansted Airport said:

“A security breach occurred at Stansted Airport on Sunday 4th January when some passengers that had arrived on a flight from Lisbon were mixed with passengers waiting to depart. As a result, and in accordance with procedures set by Department for Transport, all departing passengers had to be re-screened resulting in delays to flight operations.

“A full investigation is underway to establish how this breach in security occurred. This action was necessary to ensure the safety and security of passengers and staff and we apologise to those passengers inconvenienced by the disruption to their journey.”