Has HS2 become unaffordable?

Referencing work by Michael Byng suggesting HS2 will cost much more than expected, PT’s Whitehall Insider asks: “Since Michael Byng seems to be something of an expert in costing railway projects, shouldn’t we be taking his latest estimates very seriously indeed? And shouldn’t we be asking ourselves one simple, but now politically toxic, question? When does HS2 become unaffordable?”