Up to now the scope and quality of the art collection amassed by Roman Abramovich and Dasha Zhukova has not been in public view. Gossipy as the art world is, only a few highlights such as Lucian Freud’s Benefits Supervisor Sleeping, Paula Rego’s The Policeman’s Daughter and David Hockney’s Beverly Hills Housewife had been reported as among the acquisitions.

Yet, as the Oligarch Files reveal, in the space of a decade the former owner of Chelsea football club and his ex-wife appear to have created one of the world’s most Impressive Private Stores of modern art.

When the National Gallery cleared its halls for an ambitious exhibition of Freud’s piercingly observant portraits that opened in October 2022, it unexpectedly divided critics. Instead of the universal acclaim you might expect for this grand survey, some were underwhelmed.

Then again, important pieces were missing. It appears the Freuds collected by Abramovich and Zhukova, some of the best in private hands, were offered on loan to the show but by the time it was hung he had been subjected to sanctions as an associate of Vladimir Putin. Who would have thought the invasion of Ukraine might affect Freud’s reputation?

The Freuds – there are two more as well as Benefits Supervisor Sleeping – are it seems just the cream of the collection. This is a treasury of truly important masterpieces of the 20th and 21st centuries that gravitates towards the intellectually demanding, from the Russian pioneer of abstraction Kazimir Malevich to living heavyweights such as Anselm Kiefer, Gerhard Richter and Jasper Johns.

The disappearance of their works now into a limbo of offshore trusts and secure warehouses is a huge public loss. It is particularly devastating for British art. Abramovich and Zhukova seem to have an eye for the visceral objectivity of modern British figurative painters: Rego’s savage Dog Woman is another treasure in the hoard along with paintings by Frank Auerbach, Leon Kossoff and Peter Doig.

Abramovich appears to have assembled a better collection of the very best recent British work than the Tate

Rego died in 2021, Freud in 2011, and both are widely seen as greats. Yet as their places in art’s pantheon are posthumously settled it is critical to see and assess their masterpieces. There’s no doubt The Policeman’s Daughter and Dog Woman are in the top five Regos. How can she be fully understood if they are not on show? These two masterpieces are essential to feeling the bite and power of her imagination at its best.

To put it bluntly, Abramovich appears to have assembled a better collection of the very best recent British work than the Tate. Without these paintings by Freud, Rego and their contemporaries we can never truly grasp the British achievement in art since 1945. And while these works were prominently shown in British galleries as recently as 2021 they have become invisible since Russia attacked Ukraine.

Before European and British sanctions, Abramovich was loaning widely yet also treating his private residences as personal museums, hanging early 20th-century classics by Matisse and Picasso in his 1920s villa in the south of France, while intense contemporary art including Richter and Auerbach gave stylish seriousness to his London home.

The cultural, as opposed to financial, value of works such as the great Austrian artist of expression and eroticism Egon Schiele’s Woman in Green Slippers is beyond doubt. This is a treasury of history and aesthetic splendour, from some of the most pungent modern paintings of the human body to visions of the abstract absolute. For so many tremendous works to remain permanently out of view would leave modern culture full of holes.

Much harder to guess are the real motivations and tastes of Abramovich and Zhukova. At first sight this is a passionate, individualist collection by people with a confident eye. Freud, yes, but Auerbach? That’s discerning rather than fashionable. You may even see a political agenda in the collectors’ choice of Russian art that is at odds with Putin’s religious conservative nationalism. Abramovich and Zhukova have bought what amounts to a history of Russian modernism including the Russian futurist Natalia Goncharova, right up to Kabakov’s art that satirises dictatorship. And Zhukova has openly criticised the invasion of Ukraine, stopping exhibitions at The Garage in Moscow.

Yet the deeper you look, the less sure you can be of what this collection means to Abramovich. The sheer expense is so staggering it starts to seem as if quality is just equated with price. Cindy Sherman’s Untitled Film Stills, in which she posed as a Hitchcock heroine, are powerful but they are photographic multiples: why pay more than $3m for one particular print of a reproducible image? At least this is more understandable than the $7,669,845 spent on the overrated Richard Prince’s dumb canvas Surf Safari Nurse.

There is a sense of industrial-scale acquisition of art that’s practically guaranteed to keep or increase its value

This equation of expense and excellence goes with an appetite for safe and steady masters. The files list three Picassos, all superb, although none adopts a new style or does something startling: you could call them average Picassos, if such a thing exists. Ditto works by Matisse, Modigliani, Kandinsky. All are good investments, blue-chip stalwarts, rather than daring expressions of personal enthusiasm. So museum quality, yes – but some of the collection also has the anonymity of a museum.

The records include details of dealings with Sandy Heller, one of New York’s leading “art advisers” whose job is to identify and help purchase collectible art: it adds to the sense of industrial-scale acquisition of art that is practically guaranteed to keep or increase its value. A contract between an Abramovich company and Heller’s firm refers to “the Investor”, who is “engaged in the purchase and sale of items of tangible personal property (‘Art Property’)”.

Is this phenomenal hoard of modern art, then, just a calculated investment by an oligarch with a knack for acquiring prestigious properties, whether they are football clubs or Freuds? If that haul includes some of the finest masterpieces of today’s art it also means every time a museum has exhibited these works or a critic praised them, the prestige added to an oligarch’s cultural capital. “The wickedness of Paula Rego’s imagination shines like patent leather in her 1987 painting The Policeman’s Daughter,” I began an appreciation in the Guardian after Rego’s death last year. Ching ching!