While precise estimates are hard to come by- the simple answer to your question is yes.

The primary reason we do not know for sure is the UK Land Registry (wherein land owners are named) does not cover the whole of Britain. Ownership of land only needs be declared if the land is sold and a new buyer takes it, so land that existed before its establishment often is owned by unknown people.

Given it has remained in these mysterious hands for so long it is a reasonable assumption that this land is in the hands of noble families.

The undeclared amount of land in the UK stands at 17%. If it is owned by nobility that would make landownership by nobles in the UK about 47% of the whole country, just shy of half of it all.

What we do know is in the hands of our Dukes?

The Boughton estate belongs to the Dukes of Buccleuch, who also happen to be the largest aristocratic land owners in the UK (they own about 240,000 aches of land in Scotland); the Dukes of Westminster own more of Britain than the Queen does- crucially the land is run via Grovsenor Estates, the private family company which manages their estates; their fortune was built upon owning huge swathes of land that became London (Mayfair and Belgravia), but now own properties in the United States, Canada, Sweden, China, Japan and more. (I believe a surprisingly large chunk of Washington DC belongs to the Duke of Westminster).

The Queen is a mammoth land owner- she does NOT own 6.6 billions ached as has been incorrectly reported several times; this land is run via Crown Estates and includes large portions of London, most of the still in use palaces; large parts of Scotland; and most of Britain’s off shore wind farms. As Duchess of Lancaster (the title of Duke of Lancaster always goes to the reigning monarch these days) she owns quite a bit of land in the industrial north-east, while the title of Duke of Cornwall always goes to the heir of the throne (in this case HRH Prince Charles) and includes areas like Dartmoor, the Isles of Scilly and of course Cornwall).

She also privately (not as monarch) owns we believe a horse farm in Kentucky and a chunk of Park Avenue in NYC.

We don’t exactly know- but the British Embassy in Washington (the largest Embassy in the US) is located next door to the Vice Presidents residence I believe and that is owned entirely by the monarch.

Beyond that? Other noble land owners? The 8th Earl of Mexborough owns 20,000 aches; the Duke of Beaufort owns 20,500 mostly in Wales; the 4th Earl of Iveagh owns 20,665 aches of farmland mostly in Suffolk (fun fact- the Earl of Iveagh family surname is Guinness- yes THAT Guinness); the Dukes of Bedford around 22,500 aches (slightly less than the Italian Count Vighignolo who owns 25,000 aches of Norfolk and is the largest foreign noble landowner); the Tempest family are not aristocracy but they have held land since Norman Times and rock in around 25,500 acres; the Earls of Lonsdale have about 35,000 acres mostly in Cumbria.

And as I said- these are just the ones we know about. Hope that answers your question about the land anyway.