The West Coast Mainline is already operating at capacity. Actally operating at more capacity that was designed in during the modernisation that caused major disruption to travel over a long period.
Modifying the route to increase the loading gauge is a non starter while it is in operation. There are little things like tunnels that would need to be closed for the odd year or two in each direction to make this happen. Doing so would reduce the line's capacity to about 20% of its current capacity.
Moving over to broad gauge, while an excellent idea, has the problem that you need to do it to every line in the country to avoid the problems that caused it to be replaced by standard gauge. Do you put containers two wide in freight trains?
Double decking might help increase passenger carrying capacity (see note above, why it won't happen)., but it does bugger all to help freight capacity, unless you go to two high container trucks.
The amount of land taken up by HS2 might seem large when viewed from a pedestrian/personal viewpoint, but it is small compared with even something like the A14 or the M1.
The way to improve our 100 year old rail infrastructure is to build new lines that are good for the next 100 years or more. That can't be done over the existing rights of way (in use, built around, croocked), so new routes need to be planned and built.
Instead of pissing and moaning about it because it offends indifidual sensibilities or won't be used by those upset by it, we should be pushing forward to get it done more rapidly so the country can benefit from it. Just like it does from the motorway network, the channel tunnel, even nuclear power stations (we need more of those as well!)
Stop being a bunch of nimbys and get out of the way of progress!