There really does seem to be a lot of “carry on regardless” going on here, that HS2 is worth it whatever it costs.
What was the BCR on the original budget, what is it currently, and what cost sends it below one?
“Running out of capacity” isn’t enough to justify massive public spending - there actually has to be a real benefit to the taxpayer for expanding capacity in excess of the cost.
I think Crossrail might have been the final straw for HS2 - not only does it demonstrate a continued inability to deliver major rail schemes to time and budget, but they have destroyed the trust of politicians with what was either a cover up or utter incompetence over knowing the progress.
Or maybe the lessons from Crossrail (and Thameslink etc) are 1) that we should be more realistic about budgets and schedules ahead of time rather than promising that such schemes can be built quickly and cheaply 2) the more we fanny around the more expensive the final bill is.