If it wins the next election, it will separate the Church of England from the state.
Its new policy calls for the final split between the Christian faith and national government, which have been intertwined since Saxon times.
Bishops will be expelled from the Lords. The state will play no role in their appointment.
The Church Commissioners, who administer billions of pounds of historic property, will no longer be represented in the Commons. Parliament will lose oversight of a church, which, like the NHS, has a role of spiritual service for the “cure of souls” for all.
This policy would be the culmination of a relentless drive to edge Christianity out of public life. The Greens might argue that this trend is progressive and inevitable.
But is it what the British public really wants?
The Greens, especially under Zack Polanski, invoke the language of populism: they claim to speak for the masses that have been neglected by the mainstream parties. But disestablishing the Church of England is far from popular.
The results of a survey released last week by Whitestone Insight shows that 58 per cent of Britons think that “Christianity has something to offer governance”.
It also finds that 52 per cent believe that if Britain continues to move away from its Christian roots, “it will be to the detriment of future generations”.
Only 25 per cent, meanwhile, called for a complete separation of church and state with no interaction between them.
And strikingly, the youngest age group were more positive about Christianity in public life than the middle-aged.
The poll suggests that the Greens are out of touch with the common understanding of how important Christianity still is to British nationhood.
While 39 per cent of people think that Britain still is a Christian country, 50 per cent accept that it was once, even if not now, a Christian country.
Many respondents agreed that the country’s morals and institutions had fragmented with the decline of Christianity in the modern age.
60 per cent said Britain had lost any “meaningful shared sense of what is right and wrong”.
The Green Party’s own core values call for “social justice” and state that “the success of a society cannot be measured by narrow economic indicators” but rather “personal freedom, social equity, health, happiness, human fulfilment”, not to mention tolerance, environmental stewardship, and regard for future generations.
It seems perverse that the Greens want to do away with Christianity: it has been a leading force for putting such ideas at the heart of national life.
Too easily have the Greens forgotten that the great developments in British social justice and environmental care have come directly from Christianity.
The founders of the National Trust (Octavia Hill, Canon Hardwicke Rawnsley) and the RSPCA (Reverend Arthur Broome) were inspired by Christianity.
It was likewise for other great 19th-century charities that revolutionised the care of the poor, children, orphaned, prisoners, sick and disabled.
The very phrase “welfare state” was coined by William Temple, an Archbishop of Canterbury.
Christianity always insisted that all humans had inalienable value, and that social bonds were necessary for society to flourish.
Even British ideas of religious tolerance grew out of Christianity, with the post-Reformation concept that freedom of conscience – even to follow other faiths provided one obeyed the law – was fundamental for honest Christian adherence, and that a Christian state would guarantee such freedom as a bulwark for religion.
The Greens’ ultra-liberal policies – gender self-ID, drug liberalisation, open borders – where the satisfaction of the self trumps society can only undermine the party’s own underlying values.
The rejection of Christianity is the apotheosis of this self-destructive tendency, as all the principles the Greens claim to profess are themselves Christian in origin and character.
Can anyone be confident that Britain will maintain its moderate and cohesive character if the Greens purge Christianity from the state?
Can a secularised state stand up to the emboldened radical Islamism that appears to be ever more visible in the Green Party itself?
As Christianity has been so successful in upholding the Greens’ core values, perhaps they should leave it well alone.