An investigation has been launched after a Chiltern Railways train apparently went through a red signal - resulting in a near-miss with a Tube train.

On June 21, the Chiltern Railways passenger train was heading southbound on the Metropolitan line of the London Underground network at 9.45pm when it went through a danger (red) signal without authority, the Rail Accident Investigation Branch (RAIB) has said.

The red signal was protecting a junction so a northbound train that was waiting in Chalfont and Latimer station could cross in front of the southbound train.

An automatic brake was applied after it went through the red signal - and the Chiltern Railways train stopped around 310 metres after the signal.

The driver reportedly reset the automatic brake equipment and the train continued towards Chalfont and Latimer - but because of the position of the points, it was on the northbound line.

This meant the Chiltern Railways train and the stationary Metropolitan Line train could have been involved in a crash - but the Chiltern Railways train managed to stop just metres 23 metres apart.

Fortunately no one was injured in the near-miss, but some of the track was damaged by the train heading the wrong way.

The RAIB is investigating what led up to the near-miss, the actions of the people involved and Chiltern Railways' training, competence and fitness of its drivers.

Chiltern Railways' management of risk associated with its drivers operating on the London Underground network and any other relevant underlying issues will also be examined as part of the independent investigation.

The line had be shut between Chalfont and Latimer and Chesham following the near-miss.

A spokesman for Chiltern Railways said: A Chiltern Railways train was involved in an incident late on Sunday 21st June near Chalfont & Latimer.

"This resulted in the closure of the line between Chalfont & Latimer and Chesham stations.

"At Chiltern Railways the safety of our customers and staff is our top priority. We have an excellent safety record and are working with the Rail Accident Investigation Branch to understand the causes of this incident.

"We apologise for the disruption caused to customers using Chiltern Railways and London Underground services in the area.”