In the South and Midlands it’s about capacity relief, but as you get further north (especially if they built to Scotland) it would be more about speed and contesting with flights. Combining HS2 (London to York) and HSUK (York to Glasgow) infrastructure ideas and journey times, I reckon 2h 35 London to Edinburgh and 3h London to Glasgow is possible, so you can see that there’s going to be potential competition with aviation there, especially given the wariness sometimes felt on planes.HS2's biggest problem there has been failing to point out why it's being built - that it's primarily to relieve congestion and overcrowding. The speed is effectively a bonus.