wrote:

No, I don't think ut has been posted.

Don't know if this has already been posted:

https://www.dailymail.co.uk/news/art...nched-commuter
-train-going-wrong-way-London-Tube-line-nearly-crashes.html

How on earth can this happen? Surely the chiltern driver knew what side of the
line he was on? And why didn't the tripcocks work or have they been removed
from that section of line now?

It looks like it was perhaps a track/points fault that took the Chiltern
train across a crossover towards the Chesham line. The driver duly stopped.

https://www.railnews.co.uk/news/2020/06/23-near-collision-at-chalfont-.html

THE RAIB is investigating a reported near-collision between a London
Underground train and a National Rail service on Sunday night.

An image from the scene shows a Chiltern Railways unit and a train of
Metropolitan Line S-Stock at a stand just a few metres apart at Chalfont &
Latimer, the junction for the Chesham branch.

Reports have claimed that the Chiltern train took the wrong route at a
crossover, taking it towards the Metropolitan unit, and other unconfirmed
reports say that the points and track were damaged.

Transport for London said: ‘We apologise to customers disrupted by the
closure of the Metropolitan line between Chalfont & Latimer and Chesham.
This is the result of an incident involving a Chiltern Railways train near
Chalfont & Latimer station. We are working with Chiltern Railways to
determine exactly what happened, and our engineers will repair the railway
to return it to service as quickly as possible.’

The Transport for London website was still reporting no service on the
Chesham branch on Tuesday afternoon, and attributing the suspension to a
‘track fault’.

Chiltern Railways said: ‘We have an excellent safety record and are working
with the Rail Accident Investigation Branch to understand the causes of
this incident.’