Interestingly I'd have thought REL would have been dead set *against* governement involvment
Getting *someone* to fund the Skylon spaceport was *always* one of the things I thought was risky about the project. It's a serious chunk of cash which *only* pays off if Skylon sales happen and it has to be in place *before* that happens.
Speculation is that the spec for the runway would be no worse than that of the B36 runways built in the US to carry its nuclear deterrent in the 1940's Thick (IIRC about 5' of steel reinforced concrete) and 15000' long. Uncommon but not *beyond* the state of the art.
Lewis fails to note 2 things which have a *serious* impact on the idea.
1) Skylon is *reusuable* You buy one, use it the use it *again*. Buying an F9 right now is a one shot deal. Sure they are busting their a**es to make it at least *partly* reusable but that's still got a long way to run.
2)Virgin is *not* the only player in the sub-orbital game. Xcor aerospace are getting there. While sub-orbital is a *long* way from orbital it's a pretty good place to start a *small* fully orbital launcher from. They estimate that between those "joy rides" testing of zero gee experimental kit (for deployment to orbit in a satellite or the ISS) and acting as a launch base for (small) sat launches will make a viable business model.
A brief note on propellants. The cost of *all* propellants (as a proportion of the *total* launch cost) is *literally* so small as to be an accounting error. Elon Musk stated the propellant bill for an F9 launch is about $150k. The *whole* launch cost is about $60m, so the propellant is 0.25%. The *most* expensive fuels are the storable hydrazines. The cost c$60/lb and would make quite viable WMD's in their own right
A brief note on the SABRE engine. It does *not* liquify air. It "deeply pre-cools" the air. That "slight" difference saves a hell of a lot of Hydrogen and is one of the things that makes the idea work (worked out by Alan Bond in the mid 80s on his Sinclair Spectrum according to the 1989 article in Spaceflight).