Derived from 'green envy'; a political stance based upon envy of anyone earning more than the commentator regardless of skill or ability. Perception by some that politicians are all freeloaders and worthless so not entitles to a reasonable rate of remuneration.
The 'green' may or may not be a reference to the 'greenback' US $.
Nothing to do with the environment.
Q: So, how is it that Mr.Xyz is worth £65k pa ($100,000)?
He only sits there and votes occasionally.
A: That's just green politics because no one thinks you are worth that much!