2002, "Tube Troll", ">Incident @ Hangar lane tube <", uk.transport.london http://groups.google.com/group/uk.transport.london/browse_thread/thread/9a749f81e7f414b9/04825cc24c006db5?lnk=st&q=%22one+under%22+train&rnum=3#
The twist in this tale is that the driver (who was at the back and hadn't seen anything) booked off with stress (as drivers often do after a one under) and the guard who had been driving and witnessed the whold [sic] traumatic event had to creep into work the next day and pretend that nothing had happned...

2005, "Neilw001", "'One under'", uk.transport.london http://groups.google.com/group/uk.transport.london/browse_thread/thread/2a2f71c4882d54ca/96db8446353aa28d?lnk=st&q=%22one+under%22+train&rnum=7#96db8446353aa28d
I've been on a train when some [sic] has gone under. Actually heard the thump and then the driver on the radio saying "I've got one under".

One under

Meaning

Noun

Synonyms