For a country that's broke (yeah, right..see also: Daimond Jubilee, Olympics) this is going to cost a phenomenal amount, and for what ? Literally minutes off a train journey, regardless of the damage to areas of outstanding beauty, related local wildlife and the environment in general.
It seems total madness to me to be even considering this in our present economic situation let alone the fact that it is a complete waste of time, money and the loss of more countryside. I've always said there's more mad people ouside of asylums then in them :-).