Pooling and sharing

There is, apparently, "no business case" for extending HS2 to Scotland. An HS2 "source" explains:

"There are two things to know about HS2. One, it will terminate at Euston; two, it will not link up with HS1 or Scotland. HS2 is now looking at enhancements and there may be the odd bit of new track here and there, to reduce journey times between Scotland and London. There’s no business case."

But even if that were true, were we not told that the benefit of the Union was specifically the "pooling and sharing" of resources across the nations of the UK? After all:

"When the then Transport secretary Lord Adonis launched HS2 in 2009, he claimed it would be 'the union railway, uniting England and Scotland, north and south, richer and poorer parts of our country, sharing wealth and opportunity.' "

(For the original, see Lord Adonis's speech reported at the time here).

Scotland's share of the cost of HS2 is estimated to be around £4.7bn . To build a railway that stops a couple of hundred miles from our border.

What's the business case for that?