Yapping time!
I like trains, they look cool and are fast. They are also the best and most efficient mode of transport, but we'll get to that. Also, I live near a mainline so I grew up close to a train station. This probably helped my interest grow. Now let us begin
The first thing I would like to mention is that we do not have the best rail system, nor the worst. The fastest our trains can go on our normal tracks (everything that isn't hs1) is 125mph or aboput 200kph. Compared to the rest of Euorope this isn't particularly fast. The reason for these limited speeds is mostly that the way we created our higher speeds is by upgrading existing track, which is great for track alignments and other things but not high speeds.
The second is the pending re-nationalisation. And finally that we certainly do not have the worst, but don't have the best.
Trains are very efficient, and can be coupled together to carry more people, this means a double tracked line can carry way more than a two lane road could. Increasing frequency can increase capacity even more. Trains are also very efficient as they can move more people and goods using less energy per person than a car or bus does for the same number.