How hard would it be to build HS2 Eastern Leg in full?

[Fazaar1889]

Just looked at https://www.railmaponline.com/UKIEMap.php and have seen the eastern leg, it's a fully thought-out route. Phase 1 is the most expensive (I think???) and I've heard that 2a is shovel-ready/the cheapest and thus is a low-hanging fruit to build. On the assumption that a future government builds the eastern leg in full, how hard/expensive would it be?

 

[snowball]

Well, for a start, it would require one or more major new Acts of Parliament. No legal powers exit for the NE arm beyond its first few hundred yards. And it's substantially longer than the NW arm.

 

[HSTEd]

Well there is no legal authority to build it, so you would have to go through the bill process and all that.

Whether or not the proposed route would survive appraisal given what we know about the rest of HS2 now is another question.
It would certainly require the expenditure of substantial quantities of political capital that are almost certainly not available.