Indeed. All good points, but you then use it for Brit-bashing:

So when a country like England decides to expand an airport and not build any high speed lines, you know they're ideologically against trains, but anyways.

The record of continental Europe on resisting airport expansions and air traffic expansion is not exactly unalloyed. Witness the debate over low cost airlines. Or the several held-up or delayed high-speed rail projects, including (since Chirac's reelection) in France.

Meanwhile, what you wrote about Britain (especially in the collective) is wrong. The one big anti-train PM was Thatcher. Neither predecessors nor successors were like her. On the other hand, her successors insisted on PPP schemes, which was tried big with the CTRL, which was started by the Major government and finished now. (Unfortunately the PPP model is spreading across Europe.)

That no more high-speed lines were built so far in Britain has two reasons. One is the capital effects of past policies. An upgrade of the West Coast Mainline (WCML) was deemed cheaper with little loss in benefits. (Austria four-tracks and upgrades its own Westbahn, Germany does the same to the right-shore Rhine Valley line to Basel, and Switzerland to its busiest sections West of Zürich with the same thinking.) But (not the least because of problems with implementing moving-block signalling) the WCML price tag tripled even while the project was scaled down. At the same time, the original rail track operator collapsed financially in the wake of post-Hatfield upgrades. So building long-distance rail doesn't start with a blank sheet, but a big minus.

The other reason is that building a new high-speed line across Central and Northern England is a much bigger challenge than building one across rural France or Spain. The population and existing infrastructure denisty is higher, while the settlement structure that has to be given rail access more complex. (The WCML is not really a single line but a whole network of parallel strands.) Similar challenges are the reason that Germany's high-speed network has so many gaps, or that the Japanese one (which at least can capitalise on a stretched country on which one trunk line suffices) is so expensive. Still, various plans of true high-speed lines are discussed in Britain. (I'd guess one along the ECML is most likely to be built first.)

As a final note, while high-speed rail is the answer to air travel, the development of shorter distances shouldn't be forgotten (as is often done in Europe). Infrastructure-wise, it's the Swiss railways that are in the best shape, and they have zero 300 km/h tracks. Their policy is not of a Great Leap Forward, but incremental change, which results in several smaller enhancements along the network.

combined train+air market share

Actually, on many routes, those percentages are even exceeded. There are four-plus-hour routes beating planes. The TGV to the Mediterranean  achieves shares in excess of two-thirds on three-hour relations.

countries should forbid flights between pairs of cities connected in under 3 hours.

Fully agreed. Though, if a country spends on building a rail line and traffic starts in open competition, it can force airways to cancel flights for lack of passengers. This happened again on the London-Brussels and to a lesser extent London-Paris routes after Britain built the CTRL.

_{*Lunatic*, n.
One whose delusions are out of fashion.}