UK is quite well alive with high tech, despite its rapid descent from the height of its Victorian era. Virgin Galactic is the world’s first commercial spaceline. Now, SABRE (Synergistic Air-Breathing Rocket Engine) by Reaction Engines is going to take spaceflight to a whole new level, all about increasing payload fraction for space travel to be commercially profitable and publicly affordable. It is also interesting for military fans, who already see the value of a stand-alone space force on top of an existing air force, just as the air force was originally developed as a support force for the army, which evolved later into a separate force of its own. For long-duration asymmetric missions, scramjets remain the top choice, just like bombers. Otherwise, SABRE is here to set the stage for the first generation of space fighters. UK is dangerous. It ruled the vast oceans in the 19th century and might now the immense space in the 21st century. Of course, humans are becoming more independent-minded, so a more subtle approach to colonization may have to be developed. This is bad for humanity, because if a medium-sized nation like UK can rule the world twice, it will be too encouraging and inspirational for many other similar-sized nations. Today, we have become quite convinced that only large nations can afford to compete for world domination. History has proven that this is not true.
SABRE has a specific impulse that peaks at 3,500 seconds within the atmosphere, beating typical all-rocket systems at about 450 seconds and even “typical” nuclear thermal rockets at about 900 seconds (https://en.wikipedia.org/wiki/SABRE_(rocket_engine)). Does it mean that we should abandon nuclear technology for space travel now? Definitely not. For deep space travels or even interplanetary travels, nuclear engines remain highly competitive. However, if you are always going for a fixed path, you may be able to go to Mars with SABRE, as a highly efficient first stage engine.
To actually realize space immigration, we will still need nuclear engines to build space cruise ships, capable of mass transport. It is a somewhat important national interest, just because it is still too easy for a nuclear state to terminate another state, nuclear or not, with the press of a button. Distance is your best friend, because it buys you response time, badly needed for successful interception. This is why it’s important to keep space public, without exclusive ownership by any legal person, including nations.
It’s really bad. Think North Korea. What can you do to stop them from becoming a nuclear power? If your people are smart enough, you can always become a nuclear state. No one can stop you except you. Iran is just a loser. Stop thinking that we are able to stop people from doing what they want to do.