As I replied to your colleague, a bit late for assurances that costs won't spiral, they already have. I understand the arguement about capacity increases, but how much (cost) is too much?
I support HS2 but we do need the assurance from the governance of the project that they have a robust financial business case and costs won't spiral. 
https://www.thesun.co.uk/news/10821243/boris-johnson-hs2-dithering-decision/amp/?__twitter_impression=true …
https://www.thesun.co.uk/news/10821243/boris-johnson-hs2-dithering-decision/amp/?__twitter_impression=true …-
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And I can't spell argument
End of conversation
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