Signalling problems on the Stansted Express last night left passengers stranded and missing their flights.
Some travellers reported being stuck on board the train for more than two hours after signalling problems in the Cheshunt area led to long delays.
Many missed flights leaving from Stansted airport.
An Abellio Greater Anglia spokesperson said: "We apologise to customers for the delays and cancellations to our services yesterday evening caused by a signalling problem in the Cheshunt area. Network Rail engineers worked to restore the normal service as quickly as possible and we are sorry for the inconvenience caused.
"Under the terms of our Passenger’s Charter, customers delayed by 30 minutes or more are entitled to claim reimbursement equivalent to the cost of the affected train journey by contacting our Customer Relations Department – forms are available from staffed stations or information can be obtained form our website, www.abelliogreateranglia.co.uk."
The signalling problem affected the Stansted Express and train services on the West Anglia route, to destinations such as Stansted Airport, Cambridge and Hertford East.
