I left the railway long before privatisation and was always a ‘keep ‘em rolling’ signalman. As far as stopping or slowing trains are concerned, there will always be a good reason, whether technical or human. Problems can be anything from somebody being a bit dilatory ‘phoning the box to confirm that an accommodation crossing is clear to a car driver trying to dodge the barriers, skidding and stalling on the crossing. Yes, sometimes a signalman will slightly misjudge when to put barriers down or make a movement, but mostly it is something out of their control; going to sleep and forgetting something is probably even rarer now than then. The biggest problem we faced was the b****y drivers: either not contacting you when they should or ringing incessantly for updates when you are busy, taking an inordinate time to get moving once you have given them the road, stopping short unnecessarily, etc.: I could go on..and on and…
As far as the idea of signal boxes being quiet and peaceful: well, yes, if the signalman are on the top the job and all is running as it should it may appear so. Wait until you have barrier failures, failed trains, points out of order or an idiot wandering around on the track: then you will see organised chaos.
We would have it every morning @ Portslade when on the first train of the day - papers to Worthing around 5am, he'd always bring us to a stand before clearig. You can imagine the names we called him.
You sure you weren’t being taken in under the Warning Arrangement, which might be permitted for non-passenger workings and only needed when some boxes were switched out for the night.
The whole thread does show the way the railway has changed. Even if there was a certain amount of (usually) good-natured signalman v. driver joshing, we were all part of the same organisation.