RAIL operator GNER has launched an investigation after one of its trains was forced to make an emergency stop after splitting in two.

The train, which had been travelling through Lincolnshire on the East Coast Main Line on Saturday, had 70 people on board when a faulty coupling caused two carriages to become separated.

Passengers alerted a guard who pulled an emergency cord, causing the brakes to be applied, with the two coaches separating a few metres apart.

York-based GNER denied reports that the 7.55am service was travelling at high speeds at the time and said it had been passing through signals at no more than 30mph.

Spokesman Alan Hyde explained that clips used to secure an extra carriage in the centre of the train had worked loose, but stressed that this was caused by an assembly problem and not a design fault.

He said: "The crew managed the incident superbly well and at no time was there any risk to passengers.

"We will be writing to each of the passengers to apologise for the inconvenience and they will be fully compensated."

GNER checked the rest of its diesel fleet and found no further problems.

Labour MP Peter Mandelson was on the train and was traveling to a meeting in London from his Hartlepool constituency.

After the incident, the two parts of the train each independently took the 70 passengers to Grantham and Newark to continue the rest of their journey.