AN INVESTIGATION has been launched into a dangerous incident which saw "several trains" pass over the Lamington Viaduct after it had been badly damaged by flooding.

The rail bridge, which carries the West Coast Main Line over the River Clyde, is expected to remain closed until March. It emerged last week that the viaduct had been so badly damaged by Storm Frank on December 30 that engineers had feared it was at risk of a "catastrophic collapse" before emergency repairs were carried out. In particular, severe erosion by flooding had created a "large hole" in the viaduct's foundations.

The Herald: A Virgin West Coast passenger train crossed the Lamington Viaduct after safety concerns were raisedA Virgin West Coast passenger train crossed the Lamington Viaduct after safety concerns were raised

However, it has now emerged that hours after one train driver reported an apparent dip in the track on December 31 a passenger train service en route to Glasgow Central was allowed to pass over the bridge at high speed.

In a summary of the "dangerous occurrence", the Rail Accident Investigation Branch said that it was a train driver heading south on the 6.52am Virgin West Coast service from Edinburgh Waverley to London Euston who first reported the fault - "described as a dip in the track" as he crossed the bridge at 7.35am on Hogmanay.

The Herald: Repairs are ongoing at the Lamington ViaductRepairs are ongoing at the Lamington Viaduct

In response, signallers restricted the speed limit for passing trains until track maintenance staff had arrived on site.

After inspecting the track and watching a southbound train pass at low speed, the track maintenance staff attending removed the speed restriction. They remained on site to undertake minor remedial work.

However, after observing "unusual track movement" at 8:40am, as the 5.57am Virgin West Coast service en route from Crew to Glasgow Central crossed the viaduct at high speed they immediately re-imposed temporary speed restrictions on trains in both directions.

The line was closed to all trains a few minutes later, 8.53am, after observing a large crack in on of the bridge's three supporting piers.

In a statement, the RAIB said its investigators would examine whether any safety improvements were required.

A spokesman for Network Rail said: "The safety of passengers and our workforce is of vital importance and we are already conducting our own internal review of the incident at Lamington.

"We will work closely with the RAIB as it completes its inquiry."