:"Until the Green Party actually come out and either support or oppose they shouldnt be on the list. See http://www.chilterngreenparty.org.uk/news/25/54/Concern-over-route-for-HS2.html" 
They have come out. 
To reflect that there exists a spectrum of views, I added a section for ambiguous/noncommittal positions. I looked at organisations' statements of position. 
Does The Green Party have a position?
Yes.
Is it noncommittal? 
No. It's support, in principle, for HS2 (specifically mentioned, not just high speed rail "generally").

Verbatim from the linked article:
"While HS2 is not our priority for expenditure we do support it in principle." 

If the stated position changes, that fact can be added.