A Caledonian Sleeper train caused major commuter disruption after it was forced to make an emergency stop when it overshot the platform at Edinburgh Waverley station.

Staff onboard the northbound Lowlander service, which was carrying 120 passengers, had to activate an emergency brake, bringing it to a halt at a junction several hundred yards past the platform.

The incident, on Thursday morning, meant services to London, Dunbar, North Berwick and Tweedbank were cancelled or delayed, before the train was pushed back to the platform.

The Rail Accident Investigation Branch (RAIB) has launched an investigation, which will include inspections of the scene and the train, to determine what happened.

“An RAIB inspector was deployed yesterday to gather evidence,” a spokesman said. “We will use this information to decide any further course of action.”

The Caledonian Sleeper has suffered a number of setbacks since it relaunched with a new £150m fleet in April. On its first night, both north and southbound trains rolled into Glasgow and Euston hours behind schedule.

Serco, the service’s operator, is locked in a battle with workers over what union bosses have described as “intolerable pressure on staff” following continued mishaps.

In June, it announced that new luxury carriages that would be used to supplement the lowland service would not appear until September – after the summer holiday season.

The company said it had notified the relevant authorities about Thursday’s incident but insisted on the Sleeper’s Twitter account that “early indications are that there are no technical problems with the rolling stock”.

“Our apologies to guests affected by the incident at Edinburgh this morning. Our northbound service to Edinburgh Waverley overran the platform, due to an earlier operational issue at Carstairs,” it added.

Manuel Cortes, the general secretary of the Transport Salaried Staffs’ Association, said: “Clearly this is an incredibly serious situation which calls for nothing less than the grounding of the entire new Sleeper fleet until we have the full details of what went wrong.

“No one should be playing fast and loose with faulty brakes on our railways and Serco need to wake up to that fact and act now.”