ACCIDENT investigators have said a brake problem was to after a Caledonian Sleeper train was forced to make an emergency stop when it overshot the platform at Edinburgh Waverley station.

The RAIB raised their concerns over brake failure while launching an investigation into how the Lowland Sleeper sparked an emergency at Edinburgh Waverley station.

The Rail Accident Investigation Branch said the northbound train eventually came to a halt, but over 700 yards beyond its intended stopping point.

While there was no damage or any injuries as a result of the incident the RAIB said the outcome could "potentially have been worse, had it led to a collision with another train".

Investigators say that on the approach to Edinburgh at 7.26am on August 1, the driver discovered that the train's braking performance was "well below normal" and it "failed to stop as scheduled".

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An RAIB preliminary investigation indicated that he had no control of the brakes on the coaches because a brake pipe isolating valve was in the closed position when the train left Carstairs station.

The RAIB said this meant that the only effective brakes on the train from London Euston as it approached Edinburgh were those on the locomotive, which were "insufficient to maintain control of the train".

The train was eventually brought to a standstill by the operation of an emergency device in one of the coaches by the train manager, which caused the train brakes to apply.

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

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.

The full Rail Accident Investigation Branch investigation "will identify the sequence of events that led to the incident".

The inquiry will consider:

* How the isolating valve came to be closed at Carstairs

* The preparation of the train at Carstairs, including the attachment of the locomotive and testing of the train's brakes

* How the train was driven

* The suitability of relevant procedures and working practices

* The design and approval of the brake system fitted to the Mark 5 coaches

* Any relevant underlying management or organisational factors