Where in London it would terminate is another question; one high-speed rail proposal involves making Heathrow the national high-speed rail hub, with Eurostar trains and trains going elsewhere in Britain terminating there. Which sends the message that, if you're travelling from, say, Glasgow to the continent, you're going to be changing at Heathrow anyway, so you may as well fly; not exactly encouraging environmental responsibility. (Of course, this is assuming that flying remains affordable; if not, then siting a major rail terminus at a site with an airport and not much else is just stupid planning.)
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