In 1649, when England was tearing itself apart during the civil war, a motley crew of landless commoners moved on to St George’s Hill in Surrey and began cultivating land they did not own. The leader of this group, known as the Diggers, was George Winstanley: “I took my spade and went and broke the ground … thereby declaring freedom to the creation, and that the earth must be set free from intanglements of lords and landlords, and that it shall become a common treasury for all”.

For the Diggers, the execution of the king that year was the symbolic moment when “the common people of England” cast off the “Norman yoke” and were liberated from the landowning elite that had enslaved them since the Norman conquest. Their freedom was short-lived and they were soon evicted. What’s more, the land the Diggers occupied is now dubbed “Britain’s Beverly Hills”, a gated estate of exclusive properties, of which 72 – worth £282m – are owned by companies registered in offshore tax havens.

In England, land ownership is “our oldest, darkest, best-kept secret”. Guy Shrubsole, an activist for Friends of the Earth, has dedicated the last few years to uncovering who really owns the land. Using complex datasets from the Land Registry, freedom of information requests, and other tools available thanks to EU environmental rules, he has managed to lift the veil of secrecy: “The long-term concealment of who owns England appears to me to be one of the clearest cases of a cover-up in English history.”

From the Norman conquest, when William the Conqueror divided up the country among his barons, to the enclosure of 6.8 million acres of common land between 1604 and 1914 (“a land grab of criminal proportions”), Shrubsole shows how the land has been systematically stolen from ordinary people: “Today most of us are landless.”

The aristocracy and landed gentry still own at least 30% of England and probably far more

What’s astonishing about his research is how little has changed in the last 1,000 years. His figures reveal that the aristocracy and landed gentry – many the descendants of those Norman barons – still own at least 30% of England and probably far more, as 17% is not registered by the Land Registry and is probably inherited land that has never been bought or sold. Half of England is owned by less than 1% of the population. The homeowners’ share adds up to just 5%: “A few thousand dukes, baronets and country squires own far more land than all of Middle England put together.”

Why should we be concerned? Because land is “a common resource that everyone depends on”: for food, homes and the natural landscapes that keep our air clean and provide fresh water. Land ownership is the key to tackling some of the most pressing issues facing us today – the housing crisis, the degradation of our natural environment and the growing inequality that is blighting society.

Shrubsole argues convincingly that land should be a common good used for the benefit of everyone. This requires a programme of land reform, similar to that which Scotland has pursued in the last 20 years, opening up access to land and introducing community buy-out legislation. There are now half a million acres in community ownership in Scotland, thanks to their land reform movement.

Both detective story and historical investigation, Shrubsole’s book is a passionately argued polemic which offers radical, innovative but also practical proposals for transforming how the people of England use and protect the land that they depend on – land which should be “a common treasury for all”.

• Who Owns England? is published by William Collins (£20). To order a copy go to guardianbookshop.com or call 0330 333 6846. Free UK p&p over £15, online orders only. Phone orders min p&p of £1.99.