For UK National Rail trains, where are the rules & regulations about timetabling?

The usual (not universal) rule is that train doors may close as early as 30 seconds prior to the official departure time.

However, if the train is stopping somewhere to "set down" only (i.e.: passengers can disembark, but are not supposed to board the train), it has every right to depart much earlier than the official time.

Very occasionally, the rule is broken even when operators claim to follow it: I remember the last eastbound train departing Exhibition Centre Glasgow (EXG) two minutes early!

Many train operators remove information about a train before the doors have closed, even when it is perfectly possible to make it at nothing more than a brisk walk. Ostensibly, this is to stop people running, but it actually results in people like me running all the more frantically all over the station (because the platform is unknown) looking for the train, and I often succeed in finding it (because, even if I do not know the exact platform, I can figure it out from the style of train, presence of staff with whistle, destination-board of train, &c.) and boarding it at the very last moment (if you can stick your foot between the doors when they are nearly but not fully closed, they are forced to reopen! I have learned the technique for doing this without injuring myself).

Exceptions of which I am aware:

• If you have a bicycle and are taking it on an intercity train with a dedicated bicycle compartment, you may have to be on the correct part of the platform (usually the very front or very back) earlier. For example, Abellio Greater Anglia require cyclists boarding an intercity at London Liverpool Street (LST) to be in position 5 minutes before the departure time.

• If you are boarding a Virgin trains service at London Euston (EUS), you need to be on the platform not later than 2 minutes before the departure time, because the "platform barriers" (big doors at the beginning of platforms that do not have ticket barriers) close at that point (actually, a few platforms have ticket barriers instead of these "platform barriers", so you may still be in luck).

My experience was with a London Overground service. Looking at National Rail data, it had left almost every station one minute ahead of the scheduled departure time.

When I complained to TFL, they immediately responded with what appears to be a standard "sorry about the disruption, we have to sometimes adjust or cancel services.". I asked them to escalate the issue, and they did reply - three weeks later - with a slightly better apology.

I'd complained to the watchdog by then (it's the principle!?), and four weeks later they gave me TFL's response - which does seem to be a little contradictory:

"TfL have asked me to convey their sincere apologies for the London Overground train departing earlier than the scheduled time which caused disruption to your journey. They admitted the driver has made a mistake as all trains should never leave before the scheduled time at a station.

However, in order to avoid disruptions and so that the service is regulated, the train drivers are required to depart stations at least 30 seconds prior the departure time. So for example the timetable may show a train departure for 7:34 however the train is required to depart 30 seconds before that which would show 7:33 on the service information board. However, a train should never leave more than 30 seconds before the departure time."

I never did found out London Overground's policy about departure times...