Followup to my previous post, I did some googling and I can see that you are using an old version of a patch called Chill's patch pack from 2012. That explains why you have some options I've never seen before including the day length patch.
If one in-game minute is about ten seconds, you are playing with a version of time that is "scaled down" by a factor of 6, if that makes any sense to you. That means that your trains leaving London 30 minutes apart will actually be following each other at a distance of about 5 minutes. On first glance that seems like enough of a time gap for you to avoid having any problems with the efficiency of your stations, junctions, etc. You can see how it would be a problem though if time in-game passed hundreds of times faster (so that your trains leaving 30 minutes apart would actually all be in the same station at the same time) instead of merely 6 times faster.
Basically, some things in openttd take a fixed number of ticks, even if that isn't realistic. For example loading and unloading a long train at the default time rate (72 ticks per day I think) takes multiple days, when in reality trains only stop at stations for a few minutes at a time. Since you have 121 ticks per minute, that means you should be able to fully load a train in just a minute or two (of in-game time). Does that give your trains enough time to work through your timetable? It looks like you've scheduled two minutes stop at each station on that route you just posted, which should be just barely enough according to some rough math with the above numbers (assuming a reasonable and realistic capacity for all your trains).
When I first saw this a few months ago I thought it would never work, but the more I talk to you the more I think you might actually have this totally under control.