I would happily use high - speed trains instead of flying london to EDI/GLA. If they existed. Currently they often reach 125 mph, which the japanese shinkansen could achieve in the 1960's. On some stretches, they are suppoed to reach 140 mph. To explain further, here is a comparison of journey times from wikipedia;
"Comparisons with mainline continental services suggest that Virgin and other UK operators have a long way to go in terms of both value for money and speed. Taking a typical mainline route (London to Glasgow). The best that Virgin can achieve is 4.25 hours. By comparison, a similar mainline route (Paris to Valence) takes 2 hours. Oddly, this difference is repeated (in an inverse fashion) in fare prices. An open first class return for the Virgin route is £328 by contrast it is £160 for the French/SNCF route."
Source :
http://en.wikipedia.org/wiki/Virgin_Trains
From a pax perspective, half the people who fly to (the hell that is known as) LHR from Scotland only do so, in order to connect to an international flight. Maybe that is something that could be rectified.