[Symbiote]

I think trains in Britain avoid being scheduled to leave at 00:00, it's easy enough to leave at 23:59 at that time. It's not busy. But 12:00 wouldn't be ambiguous, since that can't be 00:00 or 24:00.

It would be pronounced "twelve hundred hours" by the automated announcement systems, and 12 o'clock by people.

Example of leaving at 5:00 (a minute in) https://youtube.com/watch?v=0cg-n-GF38E

00:01 is announced as "midnight oh one". ("The train on platform nine and three quarters is the midnight oh one service to Hogsmeade, calling at Hogsmeade only. A buffet trolley of drinks and light refreshments is available on this train.")

[Symbiote]

In fact, if you look within the next 27 minutes, the departure board for Clapham Junction has most minutes around midnight, but not midnight itself.

https://traintimes.org.uk/live/CLJ