British low-cost carrier Ryanair has ordered an inquiry into how six holidaymakers were allowed to board the wrong flight.
The carrier said the passengers, who were booked on a flight to Spain but briefly boarded a service to Latvia, would be reimbursed for extra expenses incurred due to the blunder.
Painter and decorator Stephen Pritchard, from Cannock, Staffordshire, told a local paper his boarding pass was checked three times as he was ushered on to the wrong plane with his son.
"This comes at a time when they are supposed to be tightening security. It's unbelievable," he told the paper.
Pritchard had been due to travel to Almeria on the same flight as Jo Housley, from Rotherham, and her three children.
Although the two families, who did not know each other, were taken off the wrong plane before it departed, they were unable to board their intended flight at an adjacent gate.
Ryanair said the passengers had been accommodated on an alternative flight to Spain via Birmingham Airport.
"While it is the responsibility of each customer to ensure they board the correct aircraft, we have asked our handling agent at East Midlands to investigate this incident and ensure it does not recur," the airline said in a statement.
"We sincerely apologise to the customers in question, who have been transferred on to the next available flight free of charge, provided with refreshment vouchers and advised to keep receipted expenses for reimbursement of additional transport costs."