Passengers have been warned to expect disruption

They came off the tracks shortly before 2230 GMT on Thursday while travelling at a slow speed. No-one was hurt.

Train operator First ScotRail said an investigation had been launched into the incident, which will have a "significant impact" on services.

Many services to and from Waverley are affected, with the Edinburgh to Glasgow service reduced to every 30 minutes.

Extra staff

The frequency of Fife circle trains will also be reduced from four to two per hour, and they will be among the services which will start and end their journeys at Haymarket station.

Trains travelling from Dunblane and Bathgate to Edinburgh Waverley will also stop at Haymarket.

A First ScotRail spokesman said: "Disruption is being kept to the minimum possible, and we apologise for the inconvenience.

"We have extra staff in place at key stations to assist customers with their journeys."

We will work with the train operating companies to resume services as quickly as possible David Simpson Network Rail

David Simpson, Network Rail's route director, said: "Incidents of this kind are, fortunately, very rare.

"A full investigation will be carried out in order to establish why this happened and to prevent similar incidents in the future.

"We apologise to all passengers who have had their journey disrupted and assure them that we will work with the train operating companies to resume services as quickly as possible."

The coaches, which were coming to a halt when they derailed, had been due to make up a section of the Edinburgh to London sleeper.